CVE-2021-44538: Cinny Project Cinny

Critical severity, CVSS 9.8. EPSS: 2% chance of exploitation in the next 30 days.

The olm_session_describe function in Matrix libolm before 3.2.7 is vulnerable to a buffer overflow. The Olm session object represents a cryptographic channel between two parties. Therefore, its state is partially controllable by the remote party of the channel. Attackers can construct a crafted sequence of messages to manipulate the state of the receiver's session in such a way that, for some buffer sizes, a buffer overflow happens on a call to olm_session_describe. Furthermore, safe buffer sizes were undocumented. The overflow content is partially controllable by the attacker and limited to ASCII spaces and digits. The known affected products are Element Web And SchildiChat Web.

Affected products

• Cinny Project Cinny: before 1.6.0 (fixed in 1.6.0)
• Debian Debian Linux: version 9.0 only; version 10.0 only; version 11.0 only
• Matrix Element: before 1.9.7 (fixed in 1.9.7)
• Matrix JavaScript SDK: from 2.4.2, before 15.2.1 (fixed in 15.2.1)
• Matrix Olm: from 3.1.4, before 3.2.8 (fixed in 3.2.8)
• Schildi Schildichat: before 1.9.7-sc1 (fixed in 1.9.7-sc1)

Published 2021-12-14. Last modified 2026-06-17.