Summary
Workarounds
There are no known workarounds for this issue.
Identifiers
- ELEMENTSEC-2025-1636
For more information
If you have any questions or comments about this advisory, please email us at security at element.io.
Impact
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.
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Update to Synapse 1.152.1 or later.
Frequently Asked Questions
- What is CVE-2026-45076? CVE-2026-45076 is a medium-severity improper input validation vulnerability in matrix-synapse (pip), affecting versions < 1.152.1. It is fixed in 1.152.1. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- Which versions of matrix-synapse are affected by CVE-2026-45076? matrix-synapse (pip) versions < 1.152.1 is affected.
- Is there a fix for CVE-2026-45076? Yes. CVE-2026-45076 is fixed in 1.152.1. Upgrade to this version or later.
- Is CVE-2026-45076 exploitable, and should I be worried? Whether CVE-2026-45076 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-45076 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-45076? Upgrade
matrix-synapseto 1.152.1 or later.