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CVE-2021-21332

MEDIUM
Published 2021-03-26T19:55:17
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CVSS Score

V3.1
6.9
/10
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N
Base Score Metrics
Exploitability: N/A Impact: N/A

EPSS Score

v2025.03.14
0.005
probability
of exploitation in the wild

There is a 0.5% chance that this vulnerability will be exploited in the wild within the next 30 days.

Updated: 2025-06-25
Exploit Probability
Percentile: 0.652
Higher than 65.2% of all CVEs

Attack Vector Metrics

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED

Impact Metrics

Confidentiality
HIGH
Integrity
LOW
Availability
NONE

Description

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset 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. This is fixed in version 1.27.0.

Understanding This Vulnerability

This Common Vulnerabilities and Exposures (CVE) entry provides detailed information about a security vulnerability that has been publicly disclosed. CVEs are standardized identifiers assigned by MITRE Corporation to track and catalog security vulnerabilities across software and hardware products.

The severity rating (MEDIUM) indicates the potential impact of this vulnerability based on the CVSS (Common Vulnerability Scoring System) framework. Higher severity ratings typically indicate vulnerabilities that could lead to more significant security breaches if exploited. Security teams should prioritize remediation efforts based on severity, exploit availability, and the EPSS (Exploit Prediction Scoring System) score, which predicts the likelihood of exploitation in the wild.

If this vulnerability affects products or systems in your infrastructure, we recommend reviewing the affected products section, checking for available patches or updates from vendors, and implementing recommended workarounds or solutions until a permanent fix is available. Organizations should also monitor security advisories and threat intelligence feeds for updates about active exploitation of this vulnerability.

Available Exploits

No exploits available for this CVE.

Related News

No news articles found for this CVE.

Affected Products

References

GitHub Security Advisories

Community-driven vulnerability intelligence from GitHub

✓ GitHub Reviewed MODERATE

Cross-site scripting (XSS) vulnerability in the password reset endpoint

GHSA-246w-56m2-5899

Advisory Details

### Impact The password reset 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 in #9200. ### Workarounds Depending on the needs and configuration of the homeserver a few options are available: 1. Password resets can be disabled by delegating email to a third-party service (via the `account_threepid_delegates.email` setting) or disabling email (by not configuring the `email` setting). 2. If the homeserver is not configured to use passwords (via the `password_config.enabled` setting) then the affected endpoint can be blocked at a reverse proxy: * `/_synapse/client/password_reset/email/submit_token` 3. The `password_reset_confirmation.html` template can be overridden with a custom template that manually escapes the variables using [JInja2's `escape` filter](https://jinja.palletsprojects.com/en/2.11.x/templates/#escape). See the `email.template_dir` setting.

Affected Packages

PyPI matrix-synapse
ECOSYSTEM: ≥0 <1.27.0

CVSS Scoring

CVSS Score

5.0

CVSS Vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N

Advisory provided by GitHub Security Advisory Database. Published: March 26, 2021, Modified: September 30, 2024

References

Published: 2021-03-26T19:55:17
Last Modified: 2024-08-03T18:09:15.157Z
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