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Fencer Vulns
critical 9.8

CVE-2021-44538 json

The olm_session_describe function in Matrix libolm before 3.2.7 is vulnerable to a buffer overflow.

published 2021-12-14 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-31369

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.0%
EPSS 2.0% chance of exploitation in 30 days, percentile 80%
public exploits
0
none known

Summary

The olm_session_describe function in Matrix libolm before 3.2.7 is vulnerable to a buffer overflow. The Olm session object represents a cryptographic channel between two parties. Therefore, its state is partially controllable by the remote party of the channel. Attackers can construct a crafted sequence of messages to manipulate the state of the receiver's session in such a way that, for some buffer sizes, a buffer overflow happens on a call to olm_session_describe. Furthermore, safe buffer sizes were undocumented. The overflow content is partially controllable by the attacker and limited to ASCII spaces and digits. The known affected products are Element Web And SchildiChat Web.

Patch / fix

  • matrix element 1.9.7
  • matrix javascript_sdk 15.2.1
  • matrix olm 3.2.8
  • schildi schildichat 1.9.7-sc1
  • cinny_project cinny 1.6.0
  • olm Debian 14, Debian 13, Debian 12 3.2.8~dfsg-1
  • thunderbird Debian 14, Debian 13, Debian 12 1:91.4.1-1

debian advisories DEBIAN-CVE-2021-44538

  • thunderbird Ubuntu 18.04 LTS 1:91.5.0+build1-0ubuntu0.18.04.1
  • thunderbird Ubuntu 20.04 LTS 1:91.5.0+build1-0ubuntu0.20.04.1
  • thunderbird Ubuntu 22.04 LTS 1:91.5.0+build1-0ubuntu1

ubuntu advisories UBUNTU-CVE-2021-44538

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • MozillaThunderbird SLE Workstation Extension 15 SP3 91.4.1-8.48.1

suse advisories SUSE-SU-2022:0058-1

  • MozillaThunderbird openSUSE Tumbleweed 91.4.1-1.1
  • MozillaThunderbird openSUSE Leap 15.3 91.4.1-8.48.1
  • zabbix Package Hub 15 SP3, openSUSE Leap 15.3 4.0.38-bp153.2.3.1

opensuse advisories openSUSE-SU-2024:11698-1openSUSE-SU-2022:0058-1

  • riot-web Alpine 3.17, Alpine 3.16, Alpine 3.15 +1 more 1.9.7-r0
  • element-web Alpine 3.24, Alpine 3.23, Alpine 3.22 +4 more 1.9.7-r0
  • thunderbird Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 91.4.1-r0

alpine advisories ALPINE-CVE-2021-44538

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libolm Arch Linux 3.2.8-1
  • element-web Arch Linux 1.9.7-1

arch linux advisories AVG-2638AVG-2639

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-44538 updated cvss 9.8

libolm: buffer overflow in olm_session_describe() via a crafted sequence of messages

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

2.00% chance of exploitation in the next 30 days, higher than 80% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P

Classification

Weakness
  • CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.