Null pointer dereference with file transfer request from unknown contacts

[dx]

Description

Receiving a file transfer request from a contact not in the contact list results in a null pointer dereference, leading to remote DoS by malicious remote clients.

Additionally, due to an incomplete fix of the issue above in BitlBee 3.5, the bitlbee-libpurple variant is still affected in 3.5.

Impact

This results in denial of service (remote crash of the BitlBee instance). Remote code execution does not seem to be possible (fixed offset)

For BitlBee servers configured in ForkDaemon mode (default) or inetd mode, the crash is limited to one user connection, who may just reconnect.

CVSS for bitlbee 3.4.2 and lower:

• Access Vector: Network
• Access Complexity: Low
• Authentication: None
• Confidentiality Impact: None
• Integrity Impact: None
• Availability Impact: Partial
• Exploitability: Functional Exploit Exists
• Remediation Level: Official Fix
• Report Confidence: Confirmed
• Target Distribution: High
• CVSS v2 score: 4.1

CVSS for bitlbee-libpurple 3.5:

• Target Distribution: Medium
• CVSS v2 score: 3.1

Affected versions

bitlbee-libpurple 3.5 or older

bitlbee (non-libpurple builds) 3.4.2 or older

Unaffected versions

bitlbee-libpurple 3.5.1 or newer

bitlbee (non-libpurple builds) 3.5 or newer

Resolution

• Upgrade to 3.5.1 (released 2017-01-30)

• For 3.5 see the attached

0001-purple-Fix-crash-on-ft-requests-from-unknown-contact.patch [not included in this email]

• For 3.4.2, 3.4.1 and 3.4 see the attached

0001-Fix-null-pointer-dereference-on-ft-attempts-3.4.x.patch [not included in this email]

• For 3.2.x and 3.2.x see the attached

0001-Fix-null-pointer-dereference-on-ft-attempts-3.0.x-3.2.x.patch [not included in this email]

Discussion

The issue from 3.4.2 and older only affects the jabber protocol, which is the only non-purple protocol which implements file transfers.

The issue that is still present in 3.5 affects any libpurple protocol that implements file transfers when used through BitlBee. It does not affect other libpurple-based clients such as pidgin.

There's no visible effect of the issue other than the crash.

References

Incomplete fix commit included in 3.5:

​https://github.com/bitlbee/bitlbee/commit/701ab8129ba9ea64f569daedca9a8603abad740f

Libpurple specific bugfix commit included in 3.5.1:

​https://github.com/bitlbee/bitlbee/commit/30d598ce7cd3f136ee9d7097f39fa9818a272441

[dx]

Made public