matrix-react-sdk vulnerable to XSS in Export Chat feature

Description

The Export Chat feature includes certain attacker-controlled elements in the generated document without sufficient escaping, leading to stored XSS.

Impact

Since the Export Chat feature generates a separate document, an attacker can only inject code run from the null origin, restricting the impact.

However, the attacker can still potentially use the XSS to leak message contents. A malicious homeserver is a potential attacker since the affected inputs are controllable server-side.

Patches

This was patched in matrix-react-sdk 3.76.0.

Workarounds

None, other than not using the Export Chat feature.

References

N/A