Vulnerability · Published Oct 19, 2020 · Assigned by mitre

CVE-2020-26891

Medium 6.1

In plain English

A medium-severity security flaw in the synapse package (Alpine). There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 1.9% (higher than 80% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS NVD)6.1Medium

Exploit odds (30 days)1.9%top 20.0% of all CVEs

Exploited in the wildNo reportsnot in CISA KEV

Attack toolingNoneno public tooling known

Official description

AuthRestServlet in Matrix Synapse before 1.21.0 is vulnerable to XSS due to unsafe interpolation of the session GET parameter. This allows a remote attacker to execute an XSS attack on the domain Synapse is hosted on, by supplying the victim user with a malicious URL to the /_matrix/client/r0/auth/*/fallback/web or /_matrix/client/unstable/auth/*/fallback/web Synapse endpoints.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Alpine:v3.20	synapse	1.21.1-r0	ALPINE-CVE-2020-26891
Alpine:v3.21	synapse	1.21.1-r0	ALPINE-CVE-2020-26891
Alpine:v3.22	synapse	1.21.1-r0	ALPINE-CVE-2020-26891
Alpine:v3.23	synapse	1.21.1-r0	ALPINE-CVE-2020-26891
Alpine:v3.24	synapse	1.21.1-r0	ALPINE-CVE-2020-26891
Debian:14	matrix-synapse	1.21.1-1	DEBIAN-CVE-2020-26891
PyPI	matrix-synapse	1.21.0	GHSA-3x8c-fmpc-5rmq
PyPI	matrix-synapse	1.21.0	PYSEC-2020-238

Affected products (as reported)

Vendor	Product	Versions
n/a	n/a	n/a

References

https://github.com/matrix-org/synapse/pull/8444 x_refsource_MISC
https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory x_refsource_MISC
https://github.com/matrix-org/synapse/releases/tag/v1.21.2 x_refsource_MISC
https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq x_refsource_CONFIRM