matrix-org/synapse · Security
Cross-site scripting (XSS) vulnerability in the fallback authentication endpoint
- GHSA ID
- GHSA-3x8c-fmpc-5rmq
- CVE ID
- CVE-2020-26891
- Severity
- medium
- Published
- Updated
- CVSS
- 6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- CVSS v3
- 6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- CVSS v4
- 5.1 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Description
Impact
The fallback authentication endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains.
Patches
This is fixed by #8444, which is included in Synapse v1.21.0.
Workarounds
If the homeserver is not configured to use reCAPTCHA, consent (terms of service), or single sign-on then the affected endpoint can be blocked at a reverse proxy:
/_matrix/client/r0/auth/.*/fallback/web/_matrix/client/unstable/auth/.*/fallback/web
CWEs
- CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
References
- https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq ↗
- https://github.com/matrix-org/synapse/pull/8444 ↗
- https://nvd.nist.gov/vuln/detail/CVE-2020-26891 ↗
- https://github.com/matrix-org/synapse/releases ↗
- https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory ↗
- https://github.com/matrix-org/synapse/releases/tag/v1.21.2 ↗
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2020-238.yaml ↗
- https://github.com/advisories/GHSA-3x8c-fmpc-5rmq ↗