matrix-appservice-irc events can be crafted to leak parts of targeted messages from other bridged rooms

Exploitation

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

CVSS

3.5 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:N/A:N

EPSS

• CVE-2023-38700: 0.60% estimated exploitation activity in the next 30 days; percentile 48.70 (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 It was possible to craft an event such that it would leak part of a targeted message event from another bridged room. This required knowing an event ID to target. Patches Please upgrade to 1.0.1. Workarounds You can set the matrixHandler.eventCacheSize config value to 0 to workaround this bug. However, this may impact performance. Credits Discovered and reported by Val Lorentz. For more information If you have any questions or comments about this advisory email us at security@matrix.org.

Published by the source

4 Aug 2023, 17:26 UTC

Last modified by the source

12 Nov 2023, 05:02 UTC

Source last checked

26 Oct 2026, 12:29 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-c7hh-3v6c-fj4q

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-c7hh-3v6c-fj4q

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# Patch Next advisory brief: CVE-2023-38700

Advisory: matrix-appservice-irc events can be crafted to leak parts of targeted messages from other bridged rooms
IDs: CVE-2023-38700, GHSA-c7hh-3v6c-fj4q
Record: https://patchnext.com/advisories/cve-2023-38700 (revision 2, source checked 26 Oct 2026, 12:29 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.5)
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 1.0.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm matrix-appservice-irc: affected <= 1.0.0; fixed in 1.0.1

## 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-c7hh-3v6c-fj4q (OSV record GHSA-c7hh-3v6c-fj4q lists affected ranges: npm matrix-appservice-irc >=0 <1.0.1 (fixed))
- Verified: https://github.com/advisories/GHSA-c7hh-3v6c-fj4q (GitHub-reviewed advisory GHSA-c7hh-3v6c-fj4q lists affected ranges: npm matrix-appservice-irc >=0 <=1.0.0)

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