Vulnerability CVE-2024-39691
Published: 2024-07-05

Description:
matrix-appservice-irc is a Node.js IRC bridge for the Matrix messaging protocol. The fix for GHSA-wm4w-7h2q-3pf7 / CVE-2024-32000 included in matrix-appservice-irc 2.0.0 relied on the Matrix homeserver-provided timestamp to determine whether a user has access to the event they're replying to when determining whether or not to include a truncated version of the original event in the IRC message. Since this value is controlled by external entities, a malicious Matrix homeserver joined to a room in which a matrix-appservice-irc bridge instance (before version 2.0.1) is present can fabricate the timestamp with the intent of tricking the bridge into leaking room messages the homeserver should not have access to. matrix-appservice-irc 2.0.1 drops the reliance on `origin_server_ts` when determining whether or not an event should be visible to a user, instead tracking the event timestamps internally. As a workaround, it's possible to limit the amount of information leaked by setting a reply template that doesn't contain the original message.

 References:
https://github.com/matrix-org/matrix-appservice-irc/security/advisories/GHSA-w9mh-5x8j-9754
https://github.com/matrix-org/matrix-appservice-irc/pull/1804
https://github.com/matrix-org/matrix-appservice-irc/commit/1835e047f269001054be4c68867797aa12372a0f
https://github.com/matrix-org/matrix-appservice-irc/blob/d5d67d1d3ea3f0f6962a0af2cc57b56af3ad2129/config.sample.yaml#L601-L604
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