CVE-2022-39249highCWE-287CWE-322

CVE-2022-39249: high-severity vulnerability in matrix-org matrix-js-sdk

Matrix Javascript SDK vulnerable to impersonation via forwarded Megolm sessions

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21Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 7.5epss 1.3%
In short

The Matrix Javascript SDK before version 19.7.0 allows attackers working with a malicious homeserver to create fake messages that appear to come from other users. The vulnerability exists because the SDK was too permissive in accepting forwarded encryption keys, making it possible to impersonate someone in encrypted conversations.

Technical detail

CVE-2022-39249 exploits a weak key forwarding validation in matrix-js-sdk's Megolm decryption mechanism. An attacker colluding with a compromised homeserver can inject forwarded session keys without proper verification, enabling message impersonation in end-to-end encrypted rooms. The fix enforces stricter acceptance policies, requiring forwarded keys to originate from previously-requested sources and verified devices, with a `trusted` flag marking decryption authenticity.

Summary generated and translated by AI from the official 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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Affected products
matrix-org · matrix-js-sdk
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