CVE-2026-45076: CWE-20: Improper Input Validation in element-hq synapse
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.
AI Analysis
Technical Summary
Synapse, an open source Matrix homeserver implementation by element-hq, had a vulnerability (CVE-2026-45076) due to improper input validation (CWE-20). In federated rooms, malicious homeservers could send specially crafted room events that disrupt Synapse's ability to deliver full history to clients paginating through room events. This results in incomplete room history display on clients. The vulnerability affects all versions before 1.152.1 and has a CVSS 4.0 score of 5.1 (medium severity). The issue is resolved in version 1.152.1.
Potential Impact
Clients connected to vulnerable Synapse servers may not receive the full history of federated rooms, leading to incomplete or missing room event data in client applications. This impacts user experience and the integrity of room history but does not indicate direct compromise or data leakage. There are no known exploits in the wild.
Mitigation Recommendations
Upgrade Synapse to version 1.152.1 or later where this vulnerability is fixed. Since the vulnerability is resolved in this official release, applying this update fully mitigates the issue. No additional mitigations are indicated.
CVE-2026-45076: CWE-20: Improper Input Validation in element-hq synapse
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 v4.0
Score 5.1medium
Affected software
pkg:github/element-hq/synapseRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Synapse, an open source Matrix homeserver implementation by element-hq, had a vulnerability (CVE-2026-45076) due to improper input validation (CWE-20). In federated rooms, malicious homeservers could send specially crafted room events that disrupt Synapse's ability to deliver full history to clients paginating through room events. This results in incomplete room history display on clients. The vulnerability affects all versions before 1.152.1 and has a CVSS 4.0 score of 5.1 (medium severity). The issue is resolved in version 1.152.1.
Potential Impact
Clients connected to vulnerable Synapse servers may not receive the full history of federated rooms, leading to incomplete or missing room event data in client applications. This impacts user experience and the integrity of room history but does not indicate direct compromise or data leakage. There are no known exploits in the wild.
Mitigation Recommendations
Upgrade Synapse to version 1.152.1 or later where this vulnerability is fixed. Since the vulnerability is resolved in this official release, applying this update fully mitigates the issue. No additional mitigations are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-05-08T18:45:10.096Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a1871ece29bf47b50124584
Added to database: 05/28/2026, 16:48:44 UTC
Last enriched: 06/04/2026, 20:26:24 UTC
Last updated: 07/31/2026, 19:22:59 UTC
Views: 44
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