# CVE-2021-44538: thunderbird: The olm_session_describe function in Matrix libolm before 3.2.7 isvulnerable to a buffer overflow

CVE-2021-44538 is fixed in 7 products on 1 platform, first by DEBIAN-CVE-2021-44538, released December 14, 2021. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2021-44538
- Priority: High
- CVSS: 9.8 (Medium)
- EPSS: 0.0200
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Dec 14, 2021

## Description

The olm_session_describe function in Matrix libolm before 3.2.7 isvulnerable to a buffer overflow. The Olm session object represents acryptographic channel between two parties. Therefore, its state ispartially controllable by the remote party of the channel. Attackers canconstruct a crafted sequence of messages to manipulate the state of thereceiver's session in such a way that, for some buffer sizes, a bufferoverflow happens on a call to olm_session_describe. Furthermore, safebuffer sizes were undocumented. The overflow content is partiallycontrollable by the attacker and limited to ASCII spaces and digits. Theknown affected products are Element Web And SchildiChat Web.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | olm Debian 12.15 (bookworm) | 3.2.8~dfsg-1 | [DEBIAN-CVE-2021-44538](https://patchblox.com/security/data/fix/linux/debian-cve-2021-44538.md) | Dec 14, 2021 |
| Linux | olm Debian 13.5 (trixie) | 3.2.8~dfsg-1 | [DEBIAN-CVE-2021-44538](https://patchblox.com/security/data/fix/linux/debian-cve-2021-44538.md) | Dec 14, 2021 |
| Linux | olm Debian 14 | 3.2.8~dfsg-1 | [DEBIAN-CVE-2021-44538](https://patchblox.com/security/data/fix/linux/debian-cve-2021-44538.md) | Dec 14, 2021 |
| Linux | thunderbird Debian 12.15 (bookworm) | 1:91.4.1-1 | [DEBIAN-CVE-2021-44538](https://patchblox.com/security/data/fix/linux/debian-cve-2021-44538.md) | Dec 14, 2021 |
| Linux | thunderbird Debian 13.5 (trixie) | 1:91.4.1-1 | [DEBIAN-CVE-2021-44538](https://patchblox.com/security/data/fix/linux/debian-cve-2021-44538.md) | Dec 14, 2021 |
| Linux | thunderbird Debian 14 | 1:91.4.1-1 | [DEBIAN-CVE-2021-44538](https://patchblox.com/security/data/fix/linux/debian-cve-2021-44538.md) | Dec 14, 2021 |
| Linux | thunderbird Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [thunderbird 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 |
| Linux | thunderbird Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [thunderbird 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 |
| Linux | thunderbird Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [thunderbird 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-thunderbird-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 |
| Linux | thunderbird Ubuntu 24.10 (oracular) | 1:91.5.0+build1-0ubuntu1 | [thunderbird 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-thunderbird-1-91.5.0-build1-0ubuntu1.md) | Jan 16, 2026 |
| Linux | thunderbird Ubuntu 25.04 (plucky) | 1:91.5.0+build1-0ubuntu1 | [thunderbird 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-thunderbird-1-91.5.0-build1-0ubuntu1.md) | Jan 16, 2026 |
| Linux | thunderbird-gnome-support Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [thunderbird-gnome-support 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-gnome-support-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 |
| Linux | thunderbird-gnome-support Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [thunderbird-gnome-support 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-gnome-support-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 |
| Linux | thunderbird-gnome-support Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [thunderbird-gnome-support 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-thunderbird-gnome-support-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 |
| Linux | thunderbird-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [thunderbird-mozsymbols 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-mozsymbols-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 |
| Linux | thunderbird-mozsymbols Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [thunderbird-mozsymbols 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-mozsymbols-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 |
| Linux | thunderbird-mozsymbols Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [thunderbird-mozsymbols 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-thunderbird-mozsymbols-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 |
| Linux | xul-ext-calendar-timezones Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [xul-ext-calendar-timezones 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-calendar-timezones-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 |
| Linux | xul-ext-calendar-timezones Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [xul-ext-calendar-timezones 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-calendar-timezones-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 |
| Linux | xul-ext-calendar-timezones Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [xul-ext-calendar-timezones 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-xul-ext-calendar-timezones-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 |
| Linux | xul-ext-gdata-provider Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [xul-ext-gdata-provider 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-gdata-provider-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 |
| Linux | xul-ext-gdata-provider Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [xul-ext-gdata-provider 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-gdata-provider-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 |
| Linux | xul-ext-gdata-provider Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [xul-ext-gdata-provider 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-xul-ext-gdata-provider-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 |
| Linux | xul-ext-lightning Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [xul-ext-lightning 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-lightning-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 |
| Linux | xul-ext-lightning Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [xul-ext-lightning 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-lightning-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 |
| Linux | xul-ext-lightning Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [xul-ext-lightning 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-xul-ext-lightning-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 |

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