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CVE-2021-40824

21
FAUCET Score

CVE-2021-40824 describes a logic error in the room key sharing functionality of Element Android and matrix-android-sdk2 versions prior to 1.2.2. This flaw allows a malicious Matrix homeserver within an encrypted room to steal encryption keys from affected clients, enabling the decryption of end-to-end encrypted messages. Rated Medium (CVSS 5.9), the vulnerability requires high attack complexity but can lead to a complete compromise of confidentiality without user interaction. There is currently no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 1.2.2CPE matchmatch criteria
cpe:2.3:a:matrix:element:*:*:*:*:*:android:*:*
< 1.2.2CPE matchmatch criteria
cpe:2.3:a:matrix:matrix-android-sdk2:*:*:*:*:*:android:*:*

CVSS Data

CVSS version used by this source: 3.1

5.9MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
NONE
Availability Impact
NONE
Exploitability Score
2.2
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.66%
Probability of exploitation in next 30 days
EPSS Percentile
47.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0066 is in the 9th percentile among its peer group of 19,956 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.0 Bluesky, 0.0 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (2)

github_advisorypatch availablevia nvd_reference
View patch
mavenpatch availablevia ghsa
Product: org.matrix.android:matrix-android-sdk2Fixed in: 1.2.2

Vendor Advisories (1)

mavenGHSA-jjmc-4p83-pp26medium

Logic error in Matrix SDK for Android

May 24, 2022

References

github.com / matrix-org/matrix-android-sdk2/releases/tag/v1.2.2
PatchThird Party Advisory
matrix.org / blog/2021/09/13/vulnerability-disclosure-key-sharing
Vendor Advisory