Impact

A malicious user can upload an SVG image containing JavaScript to their server. When matrix-media-repo is asked to serve that media via the /_matrix/media/(r0|v3)/download endpoint, it would be served with a Content-Disposition of inline. This can allow JavaScript to run in the browser if a client links to the /download endpoint directly.

Server operators which do not share a domain between matrix-media-repo and other services are not affected, but are encouraged to upgrade regardless.

Patches

t2bot/matrix-media-repo@77ec235 and t2bot/matrix-media-repo@bf8abdd fix the issue. Operators should upgrade to v1.3.0 as soon as possible.

Workarounds

The Content-Disposition header can be overridden by the reverse proxy in front of matrix-media-repo to always use attachment, defeating this issue at the cost of "worse" user experience when clicking download links.

References

https://developer.mozilla.org/en-US/docs/Web/SVG/Element/script

References

• GHSA-5crw-6j7v-xc72
• t2bot/matrix-media-repo@77ec235
• t2bot/matrix-media-repo@bf8abdd
• https://developer.mozilla.org/en-US/docs/Web/SVG/Element/script
• https://nvd.nist.gov/vuln/detail/CVE-2023-41318