5.1

CVE-2026-45076: element-hq synapse Improper Input Validation

CVSS: 5.1v4.0MediumAnalyzed
AliasesGHSA-6qf2-7x63-mm6vPYSEC-2026-194UBUNTU-CVE-2026-45076
Published 28-05-2026Last modified 02-06-2026
Open JSON

Vulnerability summary

CVE-2026-45076 is a medium (CVSS 5.1) Improper Input Validation vulnerability in element-hq synapse. EPSS estimates a 0.39% chance of exploitation in the next 30 days, higher than 31% of scored vulnerabilities.

Overall risk
20/100
0100
Low · default modelHow is this calculated?
CVSS score
5.1/10
010
Medium · v4.0 (CVE.org)
EPSS score
0.39%
0%100%
Low · +0.02 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 1 · Related 2
OPENSUSE-SU-2026:10898-1CGA-JX7F-G5VJ-6W3G

Timeline

  1. 28-05-2026
    PublishedVulnerability first disclosed.
  2. 02-06-2026
    Last modifiedVulnerability information updated.

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.

CVSS metrics

8 scores · 6 sources · 2 versions

EPSS trend

Probability

0.39%

Chance of exploitation in the next 30 days

Percentile

31%

Versus all other CVEs

30-day change

+0.02 pp

From 0.37% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.39%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Chainguard1 product
  • synapse< 1.153.0-r0
Debian1 product
  • matrix-synapse< 1.152.1-1
Element1 product
Element-hq1 product
PyPI1 product
  • matrix-synapse< 1.152.1
Ubuntu1 product
  • matrix-synapseAll versions (No fix recorded)

6 vendors · 6 products

References

8 links