# CVE-2021-34813: libolm3: Matrix libolm before 3.2.3 allows a malicious Matrix homeserver to crash a client (while it is attempting to retrieve...

CVE-2021-34813 is fixed in 2 products on 1 platform, first by libolm3 3.1.3+dfsg-2ubuntu0.1~esm1, released June 16, 2021. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-34813
- Priority: Routine
- CVSS: n/a (Medium)
- EPSS: 0.0426
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 16, 2021

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libolm3 Ubuntu 20.04 LTS (focal) | 3.1.3+dfsg-2ubuntu0.1~esm1 | [libolm3 3.1.3+dfsg-2ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libolm3-3.1.3-dfsg-2ubuntu0.1-esm1.md) | Jun 16, 2021 |
| Linux | python3-olm Ubuntu 20.04 LTS (focal) | 3.1.3+dfsg-2ubuntu0.1~esm1 | [python3-olm 3.1.3+dfsg-2ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-python3-olm-3.1.3-dfsg-2ubuntu0.1-esm1.md) | Jun 16, 2021 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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