Impact

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.

Patches

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.

Workarounds

It's possible to limit the amount of information leaked by setting a reply template that doesn't contain the original message. See these lines in the configuration file.

References

• Patch: matrix-org/matrix-appservice-irc#1804

For more information

If you have any questions or comments about this advisory, please email us at security at matrix.org.

References

• GHSA-w9mh-5x8j-9754
• matrix-org/matrix-appservice-irc#1804
• matrix-org/matrix-appservice-irc@1835e04
• https://nvd.nist.gov/vuln/detail/CVE-2024-39691
• https://github.com/matrix-org/matrix-appservice-irc/blob/d5d67d1d3ea3f0f6962a0af2cc57b56af3ad2129/config.sample.yaml#L601-L604