HIGH7.5

PYSEC-2026-664

Matrix Synapse Security Filtering Flaw

Quick fix

PYSEC-2026-664 — matrix-synapse: upgrade to the fixed version with the command below.

pip install --upgrade 'matrix-synapse>=0.31.1'

Details

The `on_get_missing_events` function in handlers/federation.py in Matrix Synapse before 0.31.1 has a security bug in the get_missing_events federation API where event visibility rules were not applied correctly.

Are you affected?

Enter the version of the package you're using.

Affected packages

PyPI/matrix-synapse

Introduced in: 0Fixed in: 0.31.1

Fixpip install --upgrade 'matrix-synapse>=0.31.1'

References

https://nvd.nist.gov/vuln/detail/CVE-2018-12291[ADVISORY]
https://github.com/matrix-org/synapse/pull/3371[WEB]
https://github.com/matrix-org/synapse/commit/0834b49c6a9b6c597a154d4b2dfcf8fff90699ec[WEB]
https://github.com/matrix-org/synapse[PACKAGE]
https://github.com/matrix-org/synapse/releases/tag/v0.31.1[WEB]
https://pypi.org/project/matrix-synapse[PACKAGE]
https://github.com/advisories/GHSA-v8wm-g9f2-xjv4[ADVISORY]