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CVE-2020-26891

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Date: October 19, 2020

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.

Language: Python

Severity Score

Related Resources (9)

https://github.com/matrix-org/synapse/pull/8444
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/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq
https://github.com/matrix-org/synapse/releases
https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2020-238.yaml
https://nvd.nist.gov/vuln/detail/CVE-2020-26891
https://github.com/matrix-org/synapse
https://www.mend.io/vulnerability-database/CVE-2020-26891

Severity Score

Weakness Type (CWE)

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CWE-79

Top Fix

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Upgrade to version matrix-synapse - 1.21.0

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CVSS v3.1

Base Score:
Attack Vector (AV): NETWORK
Attack Complexity (AC): LOW
Privileges Required (PR): NONE
User Interaction (UI): REQUIRED
Scope (S): CHANGED
Confidentiality (C): LOW
Integrity (I): LOW
Availability (A): NONE

CVSS v2

Base Score:
Access Vector (AV): NETWORK
Access Complexity (AC): MEDIUM
Authentication (AU): NONE
Confidentiality (C): NONE
Integrity (I): PARTIAL
Availability (A): NONE
Additional information:

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