CVE-2021-34813

Name: CVE-2021-34813
Creator: NVD / NIST
Published: 2021-06-16T18:15:09.73+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 4.26%

Last modified Jun 17, 2026

CVE-2021-34813 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. 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.. EPSS estimates a 4.26% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

4.26%

89.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-787

Affected Software

Vendor	Product	Versions
Matrix	Olm	< 3.2.3

References

https://gitlab.matrix.org/matrix-org/olm/-/commit/ccc0d122ee1b4d5e5ca4ec1432086be17d5f901bPatch, Vendor Advisory
https://gitlab.matrix.org/matrix-org/olm/-/releases/3.2.3Release Notes, Vendor Advisory
https://matrix.org/blog/2021/06/14/adventures-in-fuzzing-libolmExploit, Patch, Vendor Advisory
https://gitlab.matrix.org/matrix-org/olm/-/commit/ccc0d122ee1b4d5e5ca4ec1432086be17d5f901bPatch, Vendor Advisory
https://gitlab.matrix.org/matrix-org/olm/-/releases/3.2.3Release Notes, Vendor Advisory
https://matrix.org/blog/2021/06/14/adventures-in-fuzzing-libolmExploit, Patch, Vendor Advisory

Timeline

Published: Jun 16, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-34813?

How severe is CVE-2021-34813?

CVE-2021-34813 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 4.26% probability of exploitation in the next 30 days.

How do I fix CVE-2021-34813?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-34813?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST