Unblocking Stollen Mobile Phones using SS7-MaP vulnerabilities
- 1. 1 © Nokia Solutions and Networks 2015
Siddharth Rao / Silke Holtmanns / Ian Oliver / Tuomas Aura
- 2. 2 © Nokia Solutions and Networks 2015
• Background of SS7 attacks
• Normal Check_IMEI procedure
• Attack scenario description
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• Telecommunication systems are vulnerable.
• Recent attacks
• Core network Protocol
• Signaling System #7
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• Protocol foundation to enable roaming.
• Call establishment , management and release.
• Short Message Services (SMS).
• Supplementary services.
• Toll free numbers.
• Enhanced Message Services (EMS).
• Local Number Portability (LNP).
Signaling System #7
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SS7 Attacks timeline
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SS7 Attacks impact
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Unblocking stolen mobile devices using
Exploiting the relationship between IMEI and IMSI for EIR access
- Siddharth Rao, Dr. Silke Holtmanns, Dr. Ian Oliver, Dr Tuomas Aura
- 8. 8 © Nokia Solutions and Networks 2015 Public
Normal IMEI (device ID) Check procedure
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CheckIMEI ASN Structure
Contains only IMEI.
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• Attacker has a stolen phone which is blacklisted and he knows the IMSI
(Subsriber id) which was associated with it while blocking or last use by the
victim. The attacker does not need to have the original SIM as it is sufficient
to have just the IMSI.
• Attacker has access to SS7 network.
• The Global Title (GT, “SS7 name of a node”) of the Equipment Identity
Register (EIR) is required.
• Mobile Switching Center (MSC) GT might be needed (depending on operator
• Feature and IMSI check options are enabled.
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Users loose their phones and find it again, easy ”recovery” in EIR
MSC sends IMEI (device id) along with IMSI (subscriber id) during
Initially the IMEI is checked to know the list it belongs to. If it is found
on the black list, an additional check of IMSI is made. If there is a
match between IMSI provisioned with IMEI in the EIR database (This is
the IMSI-IMEI pair in the EIR before the victim blocks his stolen
device.) with the IMSI found in MAP_CHECK_IMEI message then this
overrides the blacklist condition.
Phone no longer blacklisted.
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CheckIMEI ASN Structure
Contains IMEI and IMSI !!!!
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1. A CHECK_IMEI* is received with IMEI = 12345678901234, and IMSI =
2. An individual IMEI match is found indicating that the IMEI is on the
3. Normally required response would be Black Listed, however; because
an IMSI is present in the message, and the IMEI is on the Black List,
the IMSI is compared to the IMSI entry in the database for this IMEI.
4. In this case, the IMSI in the RTDB matches the IMSI in the query, thus
the Black Listed condition is cancelled/overridden.
5. EIR formulates a CHECK_IMEI* response with Equipment Status = 0
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• Stolen phones would have much higher value, if they are not blacklisted and can be sold
via ebay or simlar means.
Why should somebody do this?
• 1 in 10 smart-phone owners are the
victims of phone theft.
• In United States, 113 phones per minute
are stolen or lost.
$7 million worth of smart phones on
a daily basis.
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Source: Farrell, G. (2015). Preventing phone theft and robbery: the need for government action and international coordination. Crime Science, 4(1), 1-11.
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• Attack has not been observed in real networks.
• Research was done on protocol level and publicly available
• Not all EIRs affected.
• Business case exist for the attack.
• Easy to add ”Check_IMEI*” to the filter list of network internal
messages to stop this kind of attack before it appears in real.
- 18. 18 © Nokia Solutions and Networks 2015
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