# CVE-2018-12291: PYSEC-2026-664 - Matrix Synapse Security Filtering Flaw

Source: https://junglewise.ai/threats/cve-2018-12291-matrix-synapse-security-filtering-flaw  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-02  
License: CC BY 4.0 with a link back

CVE-2018-12291 · Severity: low · CVSS 3 · Published 2026-07-02

Matrix Synapse Security Filtering Flaw

Technologies: [matrix-synapse (PyPI)](https://junglewise.ai/threats/technologies/matrix-synapse). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2018-12291 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2018-12291 being exploited in the wild.

**How severe is CVE-2018-12291?** Low severity, with a CVSS score of 3, published 2 July 2026.

**Which products and versions are affected?** matrix-synapse (PyPI) ECOSYSTEM:introduced=0,fixed=0.31.1.

**Is there a fix for CVE-2018-12291?** Yes. matrix-synapse (PyPI): upgrade to 0.31.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2018-12291?** Check whether you run matrix-synapse (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- matrix-synapse (PyPI): upgrade to 0.31.1 or later

  ```sh
  pip install "matrix-synapse>=0.31.1"
  ```


## Affected products

- matrix-synapse (PyPI) ECOSYSTEM:introduced=0,fixed=0.31.1

## Identifiers

- CVE-2018-12291
- GHSA-v8wm-g9f2-xjv4
- PYSEC-2026-664

## Related threats

- [PYSEC-2026-2620 - matrix-sydent and matrix-synapse Use Cryptographically Weak PRNG](https://junglewise.ai/threats/cve-2019-11842-matrix-sydent-and-matrix-synapse-use-cryptographically-weak-prng)
- [PYSEC-2026-1614 - Synapse vulnerable to federation denial of service via malformed events](https://junglewise.ai/threats/cve-2025-30355-synapse-vulnerable-to-federation-denial-of-service-via-malformed)
- [PYSEC-2026-1610 - Synapse Matrix has a partial room state leak via Sliding Sync](https://junglewise.ai/threats/cve-2024-53867-synapse-matrix-has-a-partial-room-state-leak-via-sliding-sync)
- [Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders](https://junglewise.ai/threats/cve-2024-53863-synapse-can-be-forced-to-thumbnail-unexpected-file-formats)
- [PYSEC-2026-1611 - Synapse allows a a malformed invite to break the invitee's `/sync`](https://junglewise.ai/threats/cve-2024-52815-synapse-allows-a-a-malformed-invite-to-break-the-invitee-s-sync)