Vulnerability · Published May 28, 2026 · Assigned by GitHub_M

CVE-2026-45076Synapse pagination denial of service

Medium 5.1

In plain English

A medium-severity improper input validation in synapse from element-hq. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 31% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)5.1Medium

Exploit odds (30 days)0.4%top 69.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Alpine:v3.23	synapse	1.152.1-r0	ALPINE-CVE-2026-45076
Alpine:v3.24	synapse	1.152.1-r0	ALPINE-CVE-2026-45076
Debian:14	matrix-synapse	1.152.1-1	DEBIAN-CVE-2026-45076
PyPI	matrix-synapse	1.152.1	GHSA-6qf2-7x63-mm6v
PyPI	matrix-synapse	1.152.1	PYSEC-2026-194
Ubuntu:24.04:LTS	matrix-synapse	no fix listed	UBUNTU-CVE-2026-45076

Affected products (as reported)

Vendor	Product	Versions
element-hq	synapse	< 1.152.1

Weakness: CWE-20 · 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

References

https://github.com/element-hq/synapse/security/advisories/GHSA-6qf2-7x63-mm6v x_refsource_CONFIRM