Security readout for executives and security teams
Plain-English summary
This flaw can break the confidentiality expected from Matrix end-to-end encrypted rooms for affected Android clients. If a malicious Matrix homeserver was present in an encrypted room, it could obtain room encryption keys and read messages sent by affected clients.
Executive priority
Prioritize remediation where Matrix encrypted rooms carry sensitive business data or involve external homeservers. The main business risk is disclosure of supposedly end-to-end encrypted communications from affected Android clients.
Technical view
Element Android before 1.2.2 and matrix-android-sdk2 before 1.2.2 had a room key sharing logic error. Crafted Matrix protocol messages from a malicious homeserver in an encrypted room could cause affected clients to share keys, allowing decryption of affected clients' encrypted messages.
Likely exposure
Exposure is likely limited to users of Element Android before 1.2.2 or Android applications built with matrix-android-sdk2 before 1.2.2, especially in encrypted rooms involving homeservers outside the organization’s control.
Exploitation context
The source bundle does not show KEV listing or active exploitation evidence. Exploitation requires a malicious Matrix homeserver present in an encrypted room and crafted protocol messages. The impact is confidentiality loss, not system takeover.
Researcher notes
The provided sources identify affected products and fixed version thresholds, but do not provide CVSS, CWE, or active exploitation evidence. Analysis should stay focused on key-sharing logic and encrypted-room confidentiality impact.
Mitigation direction
- Upgrade Element Android to version 1.2.2 or later.
- Upgrade matrix-android-sdk2 dependencies to version 1.2.2 or later.
- Check Matrix advisory and release notes for any additional vendor guidance.
- Treat affected encrypted-room content as potentially exposed when a malicious homeserver participated.
Validation and detection
- Inventory Android Matrix clients and SDK versions in managed applications.
- Confirm Element Android installations are version 1.2.2 or later.
- Review encrypted rooms for participation by untrusted or unexpected homeservers.
- Verify mobile application builds no longer depend on vulnerable matrix-android-sdk2 versions.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CVE-2021-40824 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://matrix.org/blog/2021/09/13/vulnerability-disclosure-key-sharingCVE reference · x_refsource_MISC
- https://github.com/matrix-org/matrix-android-sdk2/releases/tag/v1.2.2CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.