Logic error in Matrix SDK for Android

published 2021-09-13 5 y ago modified 2026-06-17 4 mo ago also GHSA-jjmc-4p83-pp26 , EUVD-2022-4389

cvss: 5.9; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.7%; EPSS 0.7% chance of exploitation in 30 days, percentile 51%
public exploits: 0; none known

A logic error in the room key sharing functionality of Element Android before 1.2.2 and matrix-android-sdk2 (aka Matrix SDK for Android) before 1.2.2 allows a malicious Matrix homeserver present in an encrypted room to steal room encryption keys (via crafted Matrix protocol messages) that were originally sent by affected Matrix clients participating in that room. This allows the attacker to decrypt end-to-end encrypted messages sent by affected clients.

Patch / fix

fixed in 3 distros 1 links 1

maven org.matrix.android:matrix-android-sdk2 1.2.2
matrix element 1.2.2
matrix matrix-android-sdk2 1.2.2

riot-web Alpine 3.17, Alpine 3.16, Alpine 3.15 +1 more 1.8.4-r0
element-web Alpine 3.24, Alpine 3.23, Alpine 3.22 +4 more 1.8.4-r0

alpine advisories ALPINE-CVE-2021-40824

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

github.com/matrix-org/matrix-android-sdk2/releases/tag/v1.2.2 release

Exploit prediction

0.66% chance of exploitation in the next 30 days, higher than 51% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
NVD	3.1	5.9	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD	2.0	4.3	AV:N/AC:M/Au:N/C:P/I:N/A:N
GitHub	3.1	5.9	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem	package	affected	fixed in
maven	org.matrix.android:matrix-android-sdk2	<1.2.2	1.2.2

Classification

Weakness

CWE-290 Authentication Bypass by Spoofing
CWE-327 Use of a Broken or Risky Cryptographic Algorithm

References

github.com /matrix-org/matrix-android-sdk2/releases/tag/v1.2.2
web, patch, third-party-advisory
matrix.org /blog/2021/09/13/vulnerability-disclosure-key-sharing
web, vendor-advisory
nvd.nist.gov /vuln/detail/CVE-2021-40824
advisory

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.

Summary