Bug 1906330 (CVE-2020-26891)

Summary:	CVE-2020-26891 matrix-synapse: Cross-site scripting (XSS) vulnerability in the fallback authentication endpoint
Product:	[Other] Security Response	Reporter:	Michael Kaplan <mkaplan>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED UPSTREAM	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	djc
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	matrix-synapse 1.21.0	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2020-12-10 12:47:04 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1840452, 1906331
Bug Blocks:

Description Michael Kaplan 2020-12-10 09:47:16 UTC

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.

External References:

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

Comment 1 Michael Kaplan 2020-12-10 09:47:33 UTC

Created matrix-synapse tracking bugs for this issue:

Affects: fedora-all [bug 1906331]

Comment 2 Product Security DevOps Team 2020-12-10 12:47:04 UTC

This CVE Bugzilla entry is for community support informational purposes only as it does not affect a package in a commercially supported Red Hat product. Refer to the dependent bugs for status of those individual community products.