CVE-2020-26891
MEDIUM
6.1
CVSS Score
Published: October 19, 2020 at 04:47 PM UTC
Updated: June 17, 2026 at 03:08 AM UTC
1 product affected across 1 vendorSynapse
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Severity
MEDIUM6.1
Exploit prediction
EPSS 2%
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.
Remediation
No guide yetNo remediation guidance has been written for this CVE yet. What the record does show:
References (4)
x_refsource_MISCIssue TrackingPatchThird Party Advisory
Source: [email protected]
https://github.com/matrix-org/synapse/pull/8444x_refsource_MISCRelease NotesThird Party Advisory
Source: [email protected]
https://github.com/matrix-org/synapse/releases/tag/v1.21.2x_refsource_CONFIRMPatchThird Party Advisory
Source: [email protected]
https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmqx_refsource_MISCRelease NotesVendor Advisory
Source: [email protected]
https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisoryCVSS
- Attack Vector
- NETWORK
- Complexity
- LOW
- Privileges
- NONE
- User Interaction
- REQUIRED
- Scope
- CHANGED
- Confidentiality
- LOW
- Integrity
- LOW
- Availability
- NONE
Vector?
Quick Info
StatusMODIFIED
CWE
CWE-79
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