---
id: CVE-2021-21332
aliases:
  - GHSA-246w-56m2-5899
  - PYSEC-2021-133
title: Cross-site scripting (XSS) vulnerability in the password reset endpoint
summary: Cross-site scripting (XSS) vulnerability in the password reset endpoint
severity: medium
cvss: 6.9
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N'
vendor: matrix-synapse
product: matrix-synapse
ecosystem: pip
affected:
  - matrix-synapse < 1.27.0
patched:
  - matrix-synapse 1.27.0
published: '2021-03-26'
updated: '2026-07-08'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-246w-56m2-5899'
references:
  - url: >-
      https://github.com/matrix-org/synapse/security/advisories/GHSA-246w-56m2-5899
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-21332'
  - url: 'https://github.com/matrix-org/synapse/pull/9200'
  - url: >-
      https://github.com/matrix-org/synapse/commit/e54746bdf7d5c831eabe4dcea76a7626f1de73df
  - url: 'https://github.com/matrix-org/synapse'
  - url: 'https://github.com/matrix-org/synapse/releases/tag/v1.27.0'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-133.yaml
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY
tags:
  - osv
  - pip
epss: 0.01221
epssPercentile: 0.67427
ingestedAt: '2026-07-08T18:25:44.128Z'
---

## Overview

### 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

- `matrix-synapse < 1.27.0`

## Remediation

Upgrade to a patched release:

- `matrix-synapse 1.27.0`