CVE-2026-63096: Dendrite 0.13.8 SSRF via Unauthenticated Legacy Media Download Endpoint

Severity: medium (CVSS 5.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-17 · updated 2026-10-24
Weakness: CWE-918

Description

Dendrite through 0.13.8 contains a server-side request forgery vulnerability that allows unauthenticated attackers to cause the server to open outbound TLS connections to arbitrary hosts and ports by supplying an unvalidated serverName parameter to the legacy media download endpoint. 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.

Affected products

matrix-org dendrite: through 0.13.8

References

https://github.com/geo-chen/oss/blob/main/dendrite.md#finding-2-unauthenticated-ssrf-and-internal-port-scanner-via-legacy-_matrixmediar0download
https://www.vulncheck.com/advisories/dendrite-ssrf-via-unauthenticated-legacy-media-download-endpoint

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