Skip to content
Fencer Vulns
medium 6.9

CVE-2021-21332 json

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

published 2021-03-26 5 y ago modified 2026-07-08 4 mo ago also GHSA-246w-56m2-5899 , PYSEC-2021-133 , EUVD-2021-0125

cvss
6.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 68%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi matrix-synapse 1.27.0
  • matrix synapse 1.27.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-21332 updated cvss 6.9

matrix-synapse: password reset endpoint is vulnerable to XSS

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.22% chance of exploitation in the next 30 days, higher than 68% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N
NVD 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N
GitHub 3.1 6.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N

Affected packages

ecosystem package affected fixed in
pypi matrix-synapse
<1.27.0
1.27.0

Affected products

  • matrix-org synapse

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.