Malicious Matrix homeserver can leak truncated message content of messages it shouldn't have access to

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2024-39691: 0.50% estimated exploitation activity in the next 30 days; percentile 42.73 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 originserverts 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…

Published by the source

5 Jul 2024, 20:06 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:30 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-w9mh-5x8j-9754

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-w9mh-5x8j-9754

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2024-39691

Advisory: Malicious Matrix homeserver can leak truncated message content of messages it shouldn't have access to
IDs: CVE-2024-39691, GHSA-w9mh-5x8j-9754
Record: https://patchnext.com/advisories/cve-2024-39691 (revision 2, source checked 26 Oct 2026, 12:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: matrix-appservice-irc 2.0.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm matrix-appservice-irc: affected <= 2.0.0; fixed in 2.0.1

## Suggested inspection (read-only)
- `npm ls matrix-appservice-irc --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on matrix-appservice-irc.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-w9mh-5x8j-9754 (OSV record GHSA-w9mh-5x8j-9754 lists affected ranges: npm matrix-appservice-irc >=0 <2.0.1 (fixed))
- Verified: https://github.com/advisories/GHSA-w9mh-5x8j-9754 (GitHub-reviewed advisory GHSA-w9mh-5x8j-9754 lists affected ranges: npm matrix-appservice-irc >=0 <=2.0.0)

Commands are suggestions: review each one before running it.