GHSA-6263-x97c-c4gg

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Source
https://github.com/advisories/GHSA-6263-x97c-c4gg
Import Source
https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2022/09/GHSA-6263-x97c-c4gg/GHSA-6263-x97c-c4gg.json
JSON Data
https://api.osv.dev/v1/vulns/GHSA-6263-x97c-c4gg
Aliases
Published
2022-09-30T00:40:35Z
Modified
2023-11-01T04:59:47.466927Z
Severity
  • 7.5 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N CVSS Calculator
Summary
matrix-js-sdk subject to impersonated messages due to permissive key forwarding
Details

Impact

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.

Key forwarding is a mechanism allowing clients to recover from “unable to decrypt” messages when they missed the initial key distribution, at the time the message was originally sent. Examples include accessing message history before they joined the room but also when some network/federation errors have occurred.

Patches

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.

A unique exception to this rule is with the experimental MSC3061, that is forwarding room keys for past messages when invited in a room configured with the proper history visibility setting. Such key forwards are parked upon receipt and are only accepted if the SDK receives an invitation for that room from the inviter in a limited time window.

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).

Workarounds

As this attack requires coordination between a malicious homeserver and an attacker, if you trust your homeserver, no particular workaround is needed.

References

Blog post: https://matrix.org/blog/2022/09/28/upgrade-now-to-address-encryption-vulns-in-matrix-sdks-and-clients

For more information

If you have any questions or comments about this advisory, e-mail us at security@matrix.org.

References

Affected packages

npm / matrix-js-sdk

Package

Affected ranges

Type
SEMVER
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
19.7.0