CVE-2026-63096 matrix-org CVE debrief

Who should care

Users of Dendrite through version 0.13.8 should be aware of this vulnerability and take steps to mitigate it. This vulnerability could allow attackers to gain information about internal network topology. Operators, platform administrators, vulnerability management teams, and security teams should review the vulnerability and implement necessary mitigations.

Technical summary

The vulnerability exists in the legacy media download endpoint of Dendrite, where an unauthenticated attacker can supply a serverName parameter that is not validated. This allows the server to open outbound TLS connections to arbitrary hosts and ports. Attackers can exploit distinguishable error response classes and leaked internal IP addresses in error messages to perform blind port scanning and enumerate internal network topology. The vulnerability affects Dendrite through version 0.13.8.

Defensive priority

Medium priority should be given to patching this vulnerability, as it could allow attackers to gain information about internal network topology.

Recommended defensive actions

• Apply the patch for Dendrite version 0.13.8 or later
• Restrict access to the legacy media download endpoint
• Monitor for suspicious outbound TLS connections
• Implement additional security measures to protect internal network topology
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record was published on 2026-07-17T16:17:16.630Z and was last modified on 2026-07-17T19:17:19.017Z. The NVD entry is currently Deferred. The vulnerability affects Dendrite through version 0.13.8. Evidence of exploitation is limited, and defenders should verify affected deployments and review official advisories.

Official resources