Asterisk security involves properly configuring files like SIP.conf and dial plans to prevent extension hopping and restrict access. It is also important to limit the default context, monitor the system, and use secure protocols to protect privacy. Hardening the system through practices like restricting ports and disallowing everything by default improves security.

1. Asterisk Stability & SecurityAsterisk Stability & Security
with kingasteriskwith kingasterisk
Protect your investmentProtect your investment
www.kingasterisk.comwww.kingasterisk.com
Skype : kingasteriskSkype : kingasterisk

2. IntroductionIntroduction
 What if the server goes down ?What if the server goes down ?
 What if someone hacks into your 8 e1What if someone hacks into your 8 e1
asterisk server and makes calls toasterisk server and makes calls to
inmarsat ?inmarsat ?
 Inmarsat : 5 euro / min.Inmarsat : 5 euro / min.
In 24 hours, on 8 e1sIn 24 hours, on 8 e1s  1728000 euro1728000 euro

3. OverviewOverview
 Asterisk Performance UpdateAsterisk Performance Update
 Asterisk StabilityAsterisk Stability
 Asterisk SecurityAsterisk Security
 Asterisk MonitoringAsterisk Monitoring

4. Asterisk Performance UpdateAsterisk Performance Update
 Updates since Astricon 2004:Updates since Astricon 2004:
- Smaller memory footprint- Smaller memory footprint
- Less file descriptors used- Less file descriptors used
- Memory leaks found / removed- Memory leaks found / removed
- Less RTP ports opened- Less RTP ports opened
- Codec optimizations (especially Speex)- Codec optimizations (especially Speex)
- Hardware echo canceller- Hardware echo canceller
- FastAGI- FastAGI
- Realtime- Realtime
- Remote MOH- Remote MOH
- ds3000 / te411p- ds3000 / te411p
- Channel walk optimization- Channel walk optimization

6. Astertest TestlabAstertest Testlab

7. Astertest CablesAstertest Cables

8. OverviewOverview
 Asterisk Performance UpdateAsterisk Performance Update
 Asterisk StabilityAsterisk Stability
 Asterisk server monitoringAsterisk server monitoring
 Asterisk SecurityAsterisk Security

9. Asterisk StabilityAsterisk Stability
 Hardware reliabilityHardware reliability
 Software stabilitySoftware stability

10. Asterisk Stability – Hardware ReliabilityAsterisk Stability – Hardware Reliability
 What is the cost of having no PBX serviceWhat is the cost of having no PBX service
for your company ?for your company ?
 What if you are an ISP and yourWhat if you are an ISP and your
customers can’t dial out ?customers can’t dial out ?

13. Asterisk Stability – Hardware ReliabilityAsterisk Stability – Hardware Reliability
 What if you experience:What if you experience:
- power outage ?- power outage ?
- a broken HD ?- a broken HD ?
- a broken Zaptel card ?- a broken Zaptel card ?
- a broken server ?- a broken server ?
- no Internet connectivity ?- no Internet connectivity ?

14. Asterisk Stability – Hardware ReliabilityAsterisk Stability – Hardware Reliability
 Power outage:Power outage:
 Traditional phones are self powered.Traditional phones are self powered.
Solution: use a UPS to power the (PoE) phones,Solution: use a UPS to power the (PoE) phones,
the switches, PBX, modem, router,…the switches, PBX, modem, router,…
 If you have a low power PBX, the phoneIf you have a low power PBX, the phone
system could run for hours on a small UPS.system could run for hours on a small UPS.
 Don’t use Ethernet over power for missionDon’t use Ethernet over power for mission
critical phone lines.critical phone lines.

15. Asterisk Stability – Hardware ReliabilityAsterisk Stability – Hardware Reliability
 A broken HD ?A broken HD ?
 Use raid > 0Use raid > 0
 SCSI has a bigger mean time to failure.SCSI has a bigger mean time to failure.
 Flashdisks, realtime, netboot, live CD’s.Flashdisks, realtime, netboot, live CD’s.

17. Asterisk Stability – Hardware ReliabilityAsterisk Stability – Hardware Reliability
 A broken Zaptel card or a broken server ?A broken Zaptel card or a broken server ?
 Make sure you have a replacement,Make sure you have a replacement,
(maybe even hot standby) with all the(maybe even hot standby) with all the
modules you need, jumpers already set,…modules you need, jumpers already set,…

18. Asterisk Stability – Hardware ReliabilityAsterisk Stability – Hardware Reliability
 No Internet connectivity ?No Internet connectivity ?
 Spare router / modem / switch ?Spare router / modem / switch ?
 Failover Internet connection ?Failover Internet connection ?
 Failover to / from PSTN ?Failover to / from PSTN ?

19. Label all cables!!Label all cables!!

20. Asterisk Stability / Quality UpdatesAsterisk Stability / Quality Updates
Software related since Astricon ‘04Software related since Astricon ‘04
 Real CVS-stable / CVS-head (Thanks Russell!)Real CVS-stable / CVS-head (Thanks Russell!)
 Major cleanups / code audits.Major cleanups / code audits.
 New h323 channel coming (chan_ooh323)New h323 channel coming (chan_ooh323)
 Packet Loss ConcealmentPacket Loss Concealment
 IAX2 / SIP jitter buffer (mantis 3854)IAX2 / SIP jitter buffer (mantis 3854)
 A lot of libpri, chan_sip, chan_h323 changes forA lot of libpri, chan_sip, chan_h323 changes for
better compatibility / stability.better compatibility / stability.
 DUNDi (easier load balancing with round robinDUNDi (easier load balancing with round robin
DNS)DNS)
 OSPOSP
 Kernel 2.6.11.xKernel 2.6.11.x

21. Changes in hardware reliabilityChanges in hardware reliability
 New Zaptel hardware (te411p, te4xxp,New Zaptel hardware (te411p, te4xxp,
TDM, IAXy2, …).TDM, IAXy2, …).
 New drivers with a lot of bug fixes andNew drivers with a lot of bug fixes and
optimizations.optimizations.
 End of life for x100p and Tormenta cards.End of life for x100p and Tormenta cards.
 Hardware echo cancellers -> lower CPUHardware echo cancellers -> lower CPU
load -> more calls it can handle beforeload -> more calls it can handle before
asterisk turns unstable.asterisk turns unstable.

22. * reliability / stability recommendations* reliability / stability recommendations
 Use decent but not exotic hardwareUse decent but not exotic hardware
 Put Zaptel on a different PCI-bus than Nics andPut Zaptel on a different PCI-bus than Nics and
video cards.video cards.
 Read tutorials on interrupts, APIC and otherRead tutorials on interrupts, APIC and other
common problems.common problems.
 Load test your setupLoad test your setup
 Design a failover systemDesign a failover system
 Noload unused modulesNoload unused modules
 Use recent firmware Zaptel cardsUse recent firmware Zaptel cards

23. * reliability / stability recommendations* reliability / stability recommendations
 Use a stable Asterisk version.Use a stable Asterisk version.
 Take a common OS -> Linux.Take a common OS -> Linux.
 Test software upgrades in a test lab.Test software upgrades in a test lab.
 Stay away from experimental AsteriskStay away from experimental Asterisk
modules -> h323, skinny.modules -> h323, skinny.
 Don’t patch production Asterisk servers.Don’t patch production Asterisk servers.
 Keep your old Asterisk binaries after anKeep your old Asterisk binaries after an
upgrade for easy restore of known workingupgrade for easy restore of known working
versions.versions.

24. OverviewOverview
 Asterisk Performance UpdateAsterisk Performance Update
 Asterisk StabilityAsterisk Stability
 Asterisk server monitoringAsterisk server monitoring
 Asterisk SecurityAsterisk Security

25. Asterisk server monitoringAsterisk server monitoring
 NAGIOSNAGIOS
  http://karlsbakk.net/asterisk/http://karlsbakk.net/asterisk/
 
http://megaglobal.net/docs/asterisk/html/asterihttp://megaglobal.net/docs/asterisk/html/asteri
 Argus:Argus: http://argus.tcp4me.com/http://argus.tcp4me.com/
 SNMP:SNMP: http://www.faino.it/en/asterisk.htmlhttp://www.faino.it/en/asterisk.html

26. OverviewOverview
 Asterisk Performance UpdateAsterisk Performance Update
 Asterisk StabilityAsterisk Stability
 Asterisk server monitoringAsterisk server monitoring
 Asterisk SecurityAsterisk Security

27. Asterisk SecurityAsterisk Security
 Asterisk Configuration stupidityAsterisk Configuration stupidity
 Asterisk hardeningAsterisk hardening
 Privacy protectionPrivacy protection

28. Asterisk Configuration StupidityAsterisk Configuration Stupidity
 Dial plan securityDial plan security
 SIP.confSIP.conf
 IAX2.confIAX2.conf
 Manager.confManager.conf
 Billing problemsBilling problems

29. Dial plan securityDial plan security
 - Extension hopping- Extension hopping
 - CallerID based protections- CallerID based protections
 - _.- _.
 - Demo context- Demo context
 - User access to the dial plan- User access to the dial plan
 - Be careful with the default context- Be careful with the default context
 - Limit simultaneous calls- Limit simultaneous calls

30. Extension hoppingExtension hopping
 User can reach ANY extension in the currentUser can reach ANY extension in the current
context:context:
[internal][internal]
exten => intro,1,Background(question);exten => intro,1,Background(question);
exten => 1,spanish,Goto(Spanish)exten => 1,spanish,Goto(Spanish)
exten => 2,english,Goto(English)exten => 2,english,Goto(English)
exten => _XX.,1,Dial(ZAP/g1/${EXTEN});exten => _XX.,1,Dial(ZAP/g1/${EXTEN});

31. CallerID based protectionCallerID based protection
exten => _X.,1,GotoIf($[“$exten => _X.,1,GotoIf($[“$
{CALLERIDNUM}”=“32134”?3);{CALLERIDNUM}”=“32134”?3);
exten => _X.,2,Hangup();exten => _X.,2,Hangup();
exten => _X.,3,Dial(${EXTEN});exten => _X.,3,Dial(${EXTEN});
 When not explicitly defined for eachWhen not explicitly defined for each
user/channel in zapata.conf, sip.conf, iax.conf,user/channel in zapata.conf, sip.conf, iax.conf,
the user can choose his own CallerID!the user can choose his own CallerID!

32. Inappropriate use of _.Inappropriate use of _.
 _. Would match EVERYTHING!_. Would match EVERYTHING!
(also fax, hang up, invalid, timeout,….)(also fax, hang up, invalid, timeout,….)
Example:Example:
exten => _.,1,Playback(blah);exten => _.,1,Playback(blah);
exten => _.,2,Hangup;exten => _.,2,Hangup;
 Causing a FAST LOOP.Causing a FAST LOOP.
(changed in CVS-head)(changed in CVS-head)

33. demo contextdemo context
 Not a real security riskNot a real security risk
 But… Someone might play with yourBut… Someone might play with your
system and use up your bandwidth, makesystem and use up your bandwidth, make
prank calls to Digium, make Mark Spencerprank calls to Digium, make Mark Spencer
very unhappy and cause him to introducevery unhappy and cause him to introduce
you to a very big shotgun…you to a very big shotgun…

35. User access to the dialplanUser access to the dialplan
 - AMP and other GUI’s might allow the- AMP and other GUI’s might allow the
ISP’s user to change a dial plan in his ownISP’s user to change a dial plan in his own
context. E.g.: hosted PBX’scontext. E.g.: hosted PBX’s
 - Goto / GotoIf / dial(Local/…) -> context- Goto / GotoIf / dial(Local/…) -> context
hopping.hopping.
 - System -> could do anything- System -> could do anything

36. Default contextDefault context
 Example:Example:
[default][default]
Include outgoing;Include outgoing;
Include internal;Include internal;
OH OH OH, guest calls will go to the defaultOH OH OH, guest calls will go to the default
context!!!!!context!!!!!

37. Context usage:Context usage:
 A call has two legs, the used context is theA call has two legs, the used context is the
context defined for that user/channel in thecontext defined for that user/channel in the
config file for that protocol.config file for that protocol.
E.g:E.g:
- Zap to sip call:Zap to sip call:
context set in zapata.conf is usedcontext set in zapata.conf is used
- SIP to IAX2 call:SIP to IAX2 call:
context in sip.conf is usedcontext in sip.conf is used

38. Context usage:Context usage:
 In sip.conf, zapata.conf, iax2.conf…In sip.conf, zapata.conf, iax2.conf…
A default context is defined, if there is noA default context is defined, if there is no
specific context setting for this channel orspecific context setting for this channel or
user, than the default context is used!user, than the default context is used!

39. Limit simultaneous callsLimit simultaneous calls
 Sometimes you don’t want a user to make multipleSometimes you don’t want a user to make multiple
simultaneous calls.simultaneous calls.
 E.g.: prepay / calling cardsE.g.: prepay / calling cards
Solution: setgroup, checkgroup (don’t trust incominglimit.)Solution: setgroup, checkgroup (don’t trust incominglimit.)
exten => s,1,SetGroup(${CALLERIDNUM})exten => s,1,SetGroup(${CALLERIDNUM})
exten => s,2,CheckGroup(1)exten => s,2,CheckGroup(1)
Only good if the CallerID cannot be spoofed !!!!Only good if the CallerID cannot be spoofed !!!!
Consider using accountcode for this.Consider using accountcode for this.

40. Sip.confSip.conf
 Default contextDefault context
 Bindport, bindhost, bindipBindport, bindhost, bindip
 [username] vs username=[username] vs username=
 Permit, deny, maskPermit, deny, mask
 Insecure=yes, very, noInsecure=yes, very, no
 User vs peer vs friendUser vs peer vs friend
 AllowguestAllowguest
 AutocreatepeerAutocreatepeer
 PedanticPedantic
 Ospauth
 Realm
 Md5secretMd5secret
 User authentication logicUser authentication logic
 Username= vs [username]Username= vs [username]

41. Bindport, bindhost,bindipBindport, bindhost,bindip
 If you only use sip for internal calls, don’tIf you only use sip for internal calls, don’t
put bindip=0.0.0.0 but limit it to the internalput bindip=0.0.0.0 but limit it to the internal
IP.IP.
 Changing the bindport to a non 5060 portChanging the bindport to a non 5060 port
might save you from portscan sweeps formight save you from portscan sweeps for
this port.this port.

42. Permit, deny, maskPermit, deny, mask
 Disallow everything, then allow per userDisallow everything, then allow per user
the allowed hosts or ranges.the allowed hosts or ranges.
(Multiple are allowed.)(Multiple are allowed.)

43. SIP.conf – insecure optionSIP.conf – insecure option
Insecure = …Insecure = …
 No: the default, always ask for authenticationNo: the default, always ask for authentication
 Yes: To match a peer based by IP address onlyYes: To match a peer based by IP address only
and not peer.and not peer.
 Insecure=very ; allows registered hosts to callInsecure=very ; allows registered hosts to call
without re-authenticating, by ip addresswithout re-authenticating, by ip address
 Insecure=port; we don’t care if the portnumber isInsecure=port; we don’t care if the portnumber is
different than when they registereddifferent than when they registered
 Insecure=invite; every invite is accepted.Insecure=invite; every invite is accepted.

44. User vs Peer vs Friend in SIPUser vs Peer vs Friend in SIP
 USER: never registers only makes callsUSER: never registers only makes calls
 PEER: can register + can make calls.PEER: can register + can make calls.
[user1][user1]
type=usertype=user
[user1][user1]
type=peertype=peer
Is allowed and the same as type=friend if the otherIs allowed and the same as type=friend if the other
parameters are identical!!!parameters are identical!!!

45. AllowguestAllowguest=…=…
 True: unauthenticated users will arrive inTrue: unauthenticated users will arrive in
the default context as defined in sip.confthe default context as defined in sip.conf
 False: unauthenticated users will get aFalse: unauthenticated users will get a
permission denied error message.permission denied error message.
 OSP: to allow guest access for voip trafficOSP: to allow guest access for voip traffic
coming from an OSP server.coming from an OSP server.

46. autocreatepeerautocreatepeer
 The autocreatepeer option allows, if set to Yes,The autocreatepeer option allows, if set to Yes,
any SIP UA to register with your Asterisk PBX asany SIP UA to register with your Asterisk PBX as
a peer. This peer's settings will be based ona peer. This peer's settings will be based on
global options. The peer's name will be basedglobal options. The peer's name will be based
on the user part of the Contact: header field'son the user part of the Contact: header field's
URL.URL.
This is of course a very high security risk if youThis is of course a very high security risk if you
haven't got control of access to your server.haven't got control of access to your server.
 © Olle© Olle

47. PedanticPedantic
 Defaults to pedantic=noDefaults to pedantic=no
 If enabled, this might allow a denial ofIf enabled, this might allow a denial of
service by sending a lot of invites, causingservice by sending a lot of invites, causing
a lot of (slow) DNS lookups.a lot of (slow) DNS lookups.

48. RealmRealm
Realm=Asterisk; Realm for digest
authentication
; Defaults to “Asterisk"
; Realms MUST be globally unique
according to RFC 3261
; Set this to your host name or domain name

49. How is authentication done?How is authentication done?
 chan_sip.c: /* Whoever came up with thechan_sip.c: /* Whoever came up with the
authentication section of SIP can suck myauthentication section of SIP can suck my
%*!#$ for not putting an example in the%*!#$ for not putting an example in the
spec of just what it is you're doing a hashspec of just what it is you're doing a hash
on. */on. */

50. How is authentication done?How is authentication done?
 Look at FROM header in SIP message for the username:Look at FROM header in SIP message for the username:
-> browse sip.conf for a type=user with that username-> browse sip.conf for a type=user with that username
If found -> check the md5If found -> check the md5
If not found,If not found,
-> browse sip.conf for a type=peer with that username-> browse sip.conf for a type=peer with that username
-> browse sip.conf for an (registered) IP where the request is coming from-> browse sip.conf for an (registered) IP where the request is coming from
if insecure=very, no more checks are doneif insecure=very, no more checks are done
if insecure=port, if they are willing to authenticate, even if they are callingif insecure=port, if they are willing to authenticate, even if they are calling
from a different port than they registered with. (used for NAT not using thefrom a different port than they registered with. (used for NAT not using the
same port number every time).same port number every time).
otherwise, check the md5 + allow/deny.otherwise, check the md5 + allow/deny.
 If no peer found ? do we allow guest access (allowguest=true ?)If no peer found ? do we allow guest access (allowguest=true ?)
 Yes? OK, allow send it to the default context, if not reject.Yes? OK, allow send it to the default context, if not reject.

51. Secret vs md5secretSecret vs md5secret
 With SIP all passwords are md5 encryptedWith SIP all passwords are md5 encrypted
when sending the packets, but are storedwhen sending the packets, but are stored
in plaintext in sip.confin plaintext in sip.conf
 [user][user]
 Secret=blablaSecret=blabla

52. Secret vs md5secretSecret vs md5secret
 echo - n "<user>:<realm>:<secret>" | md5sumecho - n "<user>:<realm>:<secret>" | md5sum
 E.g.:E.g.:
echo -n "user:asterisk:blabla" | md5sumecho -n "user:asterisk:blabla" | md5sum
e1b588233e4bc8645cc0da24d8cb848de1b588233e4bc8645cc0da24d8cb848d
[user][user]
md5secret=e1b588233e4bc8645cc0da24d8cb848dmd5secret=e1b588233e4bc8645cc0da24d8cb848d

53. Username= vs [username]Username= vs [username]
 [username] is for authentication a client[username] is for authentication a client
connecting to asterisk.connecting to asterisk.
Username=… is to have your asteriskUsername=… is to have your asterisk
server authenticate to another SIP server.server authenticate to another SIP server.

54. Iax.confIax.conf
 auth=plaintext,md5,rsaauth=plaintext,md5,rsa
 User authentication logicUser authentication logic
 Default contextDefault context
 [username] vs username=[username] vs username=
 Permit, deny, maskPermit, deny, mask
 Bindport, bindhost, bindipBindport, bindhost, bindip
 User vs peer vs friendUser vs peer vs friend

55. iax.conf - authiax.conf - auth
 Plaintext: passes are sent in plaintextPlaintext: passes are sent in plaintext
 Md5: encrypt the password with md5Md5: encrypt the password with md5
 RSA: use public key / private key – usesRSA: use public key / private key – uses
AES.AES.

56. User vs Peer vs friendUser vs Peer vs friend
 USER: can only accept callsUSER: can only accept calls
 PEER: can only make callsPEER: can only make calls
 FRIEND: can do bothFRIEND: can do both
[user1][user1]
type=usertype=user
[user1][user1]
type=peertype=peer
Is allowed!!!Is allowed!!!

57. How is authentication done?How is authentication done?
 In iax2: (cvs-head!!)In iax2: (cvs-head!!)
Pseudocode:Pseudocode:
Is username supplied ?Is username supplied ?
-> yes -> matched against iax.conf users starting bottom to top.-> yes -> matched against iax.conf users starting bottom to top.
user found ?user found ?
-> yes : is IP in allowed / disallowed list ?-> yes : is IP in allowed / disallowed list ?
yes –> does password match ?yes –> does password match ?
yes -> does requested context match a context=… line?yes -> does requested context match a context=… line?
-> no -> is a password given ?-> no -> is a password given ?
-> yes : Asterisk will look bottom to top for a user with this password,-> yes : Asterisk will look bottom to top for a user with this password,
-> if the context matches, or there is no context specified, and the-> if the context matches, or there is no context specified, and the
host is in the allowed lists (allow / deny) then the call is accepted.host is in the allowed lists (allow / deny) then the call is accepted.
-> no: Asterisk will look bottom to top for a user without password.-> no: Asterisk will look bottom to top for a user without password.
-> if the context matches, or there is no context specified, and the-> if the context matches, or there is no context specified, and the
host is in the allowed lists (allow / deny) then the call is accepted.host is in the allowed lists (allow / deny) then the call is accepted.

59.  Add a last entry in iax.conf with noAdd a last entry in iax.conf with no
password to force nosecret access into apassword to force nosecret access into a
specific context.specific context.
 If you use realtime, don’t have any userIf you use realtime, don’t have any user
without a password and withoutwithout a password and without
permit/deny.permit/deny.

60. Manager.confManager.conf
[general][general]
enabled = yesenabled = yes
port = 5038port = 5038
bindaddr = 0.0.0.0bindaddr = 0.0.0.0
[zoa][zoa]
secret = blablasecret = blabla
deny=0.0.0.0/0.0.0.deny=0.0.0.0/0.0.0.
permit=221.17.246.77/255.255.255.0permit=221.17.246.77/255.255.255.0
permit=127.0.0.1/255.255.255.0permit=127.0.0.1/255.255.255.0
read = system,call,log,verbose,command,agent,userread = system,call,log,verbose,command,agent,user
write = system,call,log,verbose,command,agent,userwrite = system,call,log,verbose,command,agent,user

61. Manager.confManager.conf
 No encryption is used, even the passwordNo encryption is used, even the password
is sent in plaintext.is sent in plaintext.
 Don’t enable it on a public IP.Don’t enable it on a public IP.
 UseUse http://www.stunnel.org/http://www.stunnel.org/
 Watch out with management programsWatch out with management programs
with direct interface to the manager.with direct interface to the manager.
 Limit the privileges per user (especially theLimit the privileges per user (especially the
system!!!).system!!!).

62. Asterisk SecurityAsterisk Security
 Asterisk Configuration stupidityAsterisk Configuration stupidity
 Asterisk hardeningAsterisk hardening
 Privacy protectionPrivacy protection

63. Asterisk HardeningAsterisk Hardening
 Asterisk as non-root userAsterisk as non-root user
 Asterisk in CHROOTAsterisk in CHROOT
 Asterisk in a JAILAsterisk in a JAIL
 Asterisk with limited read / write permissionsAsterisk with limited read / write permissions
 ZAPTEL kernel modulesZAPTEL kernel modules
 Asterisk firewalling / shaping / NATAsterisk firewalling / shaping / NAT
 Tty9Tty9
 Linux hardeningLinux hardening
 Remote loggingRemote logging
 TripwireTripwire
 Limit running system processesLimit running system processes

64. Asterisk as non root userAsterisk as non root user
adduser --system --home /var/lib/asterisk --no-create-home Asteriskadduser --system --home /var/lib/asterisk --no-create-home Asterisk
chown -r asterisk:asterisk /var/lib/asteriskchown -r asterisk:asterisk /var/lib/asterisk
chown -r asterisk:asterisk /var/log/asteriskchown -r asterisk:asterisk /var/log/asterisk
chown -r asterisk:asterisk /var/run/asteriskchown -r asterisk:asterisk /var/run/asterisk
chown -r asterisk:asterisk /var/spool/asteriskchown -r asterisk:asterisk /var/spool/asterisk
chown -r asterisk:asterisk /dev/zapchown -r asterisk:asterisk /dev/zap
chown -r root:asterisk /etc/asteriskchown -r root:asterisk /etc/asterisk
chmod -r u=rwX,g=rX,o= /var/lib/asteriskchmod -r u=rwX,g=rX,o= /var/lib/asterisk
chmod -r u=rwX,g=rX,o= /var/log/asteriskchmod -r u=rwX,g=rX,o= /var/log/asterisk
chmod -r u=rwX,g=rX,o= /var/run/asteriskchmod -r u=rwX,g=rX,o= /var/run/asterisk
chmod -r u=rwX,g=rX,o= /var/spool/asteriskchmod -r u=rwX,g=rX,o= /var/spool/asterisk
chmod -r u=rwX,g=rX,o= /dev/zapchmod -r u=rwX,g=rX,o= /dev/zap
chmod -r u=rwX,g=rX,o= /etc/asteriskchmod -r u=rwX,g=rX,o= /etc/asterisk
chown asterisk /dev/tty9chown asterisk /dev/tty9
su asterisk -c /usr/sbin/safe_asterisksu asterisk -c /usr/sbin/safe_asterisk
oror
Asterisk -U asterisk -G asteriskAsterisk -U asterisk -G asterisk

65.  Asterisk has no write permissions for itsAsterisk has no write permissions for its
config files and is running as non root ?config files and is running as non root ?
 In the unlikely event of someone breakingIn the unlikely event of someone breaking
in through Asterisk, your dial plan is stillin through Asterisk, your dial plan is still
vulnerable through the CLI or thevulnerable through the CLI or the
manager.manager.
Asterisk with limited read / write permissionsAsterisk with limited read / write permissions

66. Asterisk in chrootAsterisk in chroot
 Changes the root directory visible toChanges the root directory visible to
asterisk to e.g. /foo/barasterisk to e.g. /foo/bar
 Pretty useless if asterisk is running as rootPretty useless if asterisk is running as root
and perl or gcc is available.and perl or gcc is available.

67. Asterisk in a jailAsterisk in a jail
 Changes the rootChanges the root
directory visible todirectory visible to
Asterisk.Asterisk.
 Limits theLimits the
commands /commands /
programs any user inprograms any user in
this jail can execute tothis jail can execute to
a list you specify.a list you specify.
 Expansion of chroot.Expansion of chroot.

68. Zaptel kernel modulesZaptel kernel modules
 Zaptel is module only, cannot be put into theZaptel is module only, cannot be put into the
kernel.kernel.
 Hackers like to hide in a module, they canHackers like to hide in a module, they can
backdoor a module, compile it, load it in memorybackdoor a module, compile it, load it in memory
and remove all traces on the disk.and remove all traces on the disk.
 You could have the kernel check an md5 for theYou could have the kernel check an md5 for the
Zaptel modules.Zaptel modules.
 I think Matt Frederickson compiled them in theI think Matt Frederickson compiled them in the
kernel before.kernel before.

69. Firewalling / shaping / NATFirewalling / shaping / NAT
 Block everything except the ports youBlock everything except the ports you
really want. (5060, 4569, …)really want. (5060, 4569, …)
 RTP ports are a big pita (see rtp.conf)RTP ports are a big pita (see rtp.conf)
Sidenote: you might want to check your ISPSidenote: you might want to check your ISP
is not blocking anything in the rangeis not blocking anything in the range
defined in RTP.confdefined in RTP.conf

70. Limit access to tty9Limit access to tty9
 safe_asterisk opens a console on tty9.safe_asterisk opens a console on tty9.
This does not require a password and willThis does not require a password and will
provide a root shell to anyone passing by.provide a root shell to anyone passing by.
(by using !command on the CLI).(by using !command on the CLI).
 Remove the offending line, or don’t useRemove the offending line, or don’t use
safe_asterisksafe_asterisk

71. Linux HardeningLinux Hardening
 GRsec (2.6.x)GRsec (2.6.x)
 Openwall (2.4.x)Openwall (2.4.x)
 Remove all unneeded things.Remove all unneeded things.

72. Remote loggingRemote logging
 Remote syslogRemote syslog
 Put Asterisk log files (and other log files onPut Asterisk log files (and other log files on
a remote server).a remote server).

73. TripwireTripwire
 Make hashes of all the important files onMake hashes of all the important files on
the server and check them for changesthe server and check them for changes
you didn’t do.you didn’t do.

74. Limit server processesLimit server processes
 An Asterisk server should be only:An Asterisk server should be only:
- OS + ASTERISK.OS + ASTERISK.
- No databaseNo database
- No APACHENo APACHE
- No PHPNo PHP
(If you really need those, and don’t have enough(If you really need those, and don’t have enough
servers, don’t put them on a public IP andservers, don’t put them on a public IP and
firewall them!!!!)firewall them!!!!)

75. Asterisk SecurityAsterisk Security
 Asterisk Configuration stupidityAsterisk Configuration stupidity
 Asterisk hardeningAsterisk hardening
 Privacy protectionPrivacy protection

76. Asterisk privacyAsterisk privacy
 EncryptionEncryption
 MonitoringMonitoring
 CallerID spoofingCallerID spoofing
 CallingPRESCallingPRES

77. Call Encryption - SIPCall Encryption - SIP
 SRTP -> method to encrypt voice packets.SRTP -> method to encrypt voice packets.
 TLS -> method to encrypt signalingTLS -> method to encrypt signaling
packets.packets.
Both are not yet supported by asterisk.Both are not yet supported by asterisk.
Bounty on voip-info.org.Bounty on voip-info.org.

78. Call Encryption – IAX2Call Encryption – IAX2
 30/12/2004 2:0730/12/2004 2:07
Modified Files: chan_iax2.c iax2-parser.cModified Files: chan_iax2.c iax2-parser.c
iax2-parser.h iax2.h Log Message: Minoriax2-parser.h iax2.h Log Message: Minor
IAX2 fixes, add incomplete-but-very-IAX2 fixes, add incomplete-but-very-
basically-functional IAX2 encryption.basically-functional IAX2 encryption.
It would support any type of encryption youIt would support any type of encryption you
like. -> Doesn’t work yet.like. -> Doesn’t work yet.

79. Call Encryption – GeneralCall Encryption – General solutionsolution
 Send you packets through a VPN orSend you packets through a VPN or
tunnel.tunnel.
 Use only UDP tunnels to avoid delays.Use only UDP tunnels to avoid delays.
Known to work:Known to work:
IPSEC, VTUN, OPENVPN.IPSEC, VTUN, OPENVPN.

80. Call Encryption – Tunnel solutionCall Encryption – Tunnel solution
Advantage, CPU expensive encryptionAdvantage, CPU expensive encryption
can happen on dedicated machine.can happen on dedicated machine.
 Disadvantage: doesn’t work onDisadvantage: doesn’t work on
hardphones or ATA’s without adding anhardphones or ATA’s without adding an
extra server in front of them.extra server in front of them.

81. MonitoringMonitoring
 ZapBargeZapBarge
 ChanSpyChanSpy
 MonitorMonitor
Thank you Very Much......!!!Thank you Very Much......!!!
For More InformationFor More Information
www.kingasterisk.comwww.kingasterisk.com