CVE-2021-34813: Matrix Olm

Critical severity, CVSS 9.8. EPSS: 4.3% chance of exploitation in the next 30 days.

Matrix libolm before 3.2.3 allows a malicious Matrix homeserver to crash a client (while it is attempting to retrieve an Olm encrypted room key backup from the homeserver) because olm_pk_decrypt has a stack-based buffer overflow. Remote code execution might be possible for some nonstandard build configurations.

Affected products

• Matrix Olm: before 3.2.3 (fixed in 3.2.3)

Published 2021-06-16. Last modified 2026-06-17.