Summary
Workarounds
If Synapse is deployed behind a reverse proxy, the reverse proxy could be configured to limit the rate of user requests,
preventing or increasing the difficulty of the attack.
Identifiers
- ELEMENTSEC-2026-1706
For more information
If you have any questions or comments about this advisory, please email us at security at element.io.
Impact
Local authenticated users can cause Synapse to starve other requests of CPU and lead to other requests failing, causing other users to be denied service.
Homeservers that trust all their local users are not at risk.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-45078 has a CVSS score of 5.5 (High). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.152.1); upgrading removes the vulnerable code path.
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-2026-45078? CVE-2026-45078 is a high-severity uncontrolled resource consumption vulnerability in matrix-synapse (pip), affecting versions < 1.152.1. It is fixed in 1.152.1. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-45078? CVE-2026-45078 has a CVSS score of 5.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of matrix-synapse are affected by CVE-2026-45078? matrix-synapse (pip) versions < 1.152.1 is affected.
- Is there a fix for CVE-2026-45078? Yes. CVE-2026-45078 is fixed in 1.152.1. Upgrade to this version or later.
- Is CVE-2026-45078 exploitable, and should I be worried? Whether CVE-2026-45078 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-2026-45078 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-2026-45078? Upgrade
matrix-synapseto 1.152.1 or later.