CVE-2021-34813

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 4.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-06-16 · updated 2026-06-17
Weakness: CWE-787

Description

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

How to fix

Upgrade to a fixed version: Matrix Olm 3.2.3. Check the vendor advisory for mitigations.

References

https://gitlab.matrix.org/matrix-org/olm/-/commit/ccc0d122ee1b4d5e5ca4ec1432086be17d5f901b
https://gitlab.matrix.org/matrix-org/olm/-/releases/3.2.3
https://matrix.org/blog/2021/06/14/adventures-in-fuzzing-libolm
https://gitlab.matrix.org/matrix-org/olm/-/commit/ccc0d122ee1b4d5e5ca4ec1432086be17d5f901b
https://gitlab.matrix.org/matrix-org/olm/-/releases/3.2.3
https://matrix.org/blog/2021/06/14/adventures-in-fuzzing-libolm

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