CVE-2023-33980

Vulnerability

The Bramble Synchronisation Protocol (BSP) in Briar before version 1.4.22 contains a logic flaw where receiving a message longer than the maximum allowed length triggers an exception of an unexpected type. Instead of raising an error that discards the message, the exception causes the app to exit. The validation is performed in memory-safe Java code, so there is no risk of memory corruption. The invalid messages are not stored or forwarded to other users [1].

Exploitation

An attacker must be a contact of the victim in the Briar app. The attacker repeatedly sends messages that exceed the maximum allowed length to the victim. Because the length check raises the wrong type of error, each malformed message causes the target's Briar app to crash [1].

Impact

Successful exploitation results in a denial of service: the victim's Briar application repeatedly crashes, preventing them from using the app. There is no evidence of data corruption, information disclosure, or privilege escalation. The crash is limited to the client application and does not affect other users or the server infrastructure [1].

Mitigation

The vulnerability was fixed in Briar 1.4.22, released in February 2023. Users are encouraged to upgrade to version 1.5.3 (released May 24, 2023) which includes fixes for all three reported issues. No workarounds have been published for unpatched versions. The developers have not received reports of exploitation in the wild [1].