CVE-2026-45076: Synapse is an open source Matrix homeserver implementation

Q: How do I fix CVE-2026-45076?

synapse: upgrade to 1.152.1. Exact commands for each OS are on this page.

Q: Is CVE-2026-45076 being exploited?

CVE-2026-45076 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-45076 affect?

CVE-2026-45076 affects synapse. Severity is low (CVSS 2.7). 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 cou

Q: How urgent is CVE-2026-45076?

Priority 17/100. No elevated risk signals yet.

Routine

LOW 2.7UPGRADE

CVE-2026-45076 is a low-severity flaw (CVSS 2.7) affecting synapse. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	2.7 (Low)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	High
User interaction	None
EPSS exploit chance	0.4% (top 69%)
CISA exploited list	No
Weakness	CWE-20
Published	2026-05-28
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: element

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-28 17:16 UTCPublished CVE record published
2026-10-26 13:10 UTCUpdated Record last modified

element synapse UPGRADE

Affected: < 1.152.1

Fixed in: 1.152.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy synapse || rpm -q synapse || synapse --version

2. UPGRADE to 1.152.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade synapse

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade synapse

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-45076?

synapse: upgrade to 1.152.1. Exact commands for each OS are on this page.

Is CVE-2026-45076 being exploited?

CVE-2026-45076 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-45076 affect?

CVE-2026-45076 affects synapse. Severity is low (CVSS 2.7). 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 cou

How urgent is CVE-2026-45076?

Priority 17/100. No elevated risk signals yet.

Related CVEs

CVE-2026-45078 MEDIUM 5.5 UPGRADE Synapse is an open source Matrix homeserver implementation

References

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