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) affecting versions before 1.152.1. In federated rooms, malicious homeservers could send specially crafted room events that interfere with Synapse's ability to serve full room history to clients using pagination. This improper input validation (CWE-20) causes clients to miss parts of the room history. The vulnerability has a CVSS 4.0 base score of 5.1 (medium severity) and was fixed in version 1.152.1.
Potential Impact
Clients connected to vulnerable Synapse servers may not receive the full history of federated rooms, potentially impacting user experience and completeness of chat history. There is no indication of data compromise or remote code execution. The impact is limited to incomplete room history display.
Mitigation Recommendations
Upgrade Synapse to version 1.152.1 or later, where this vulnerability is fixed. Since the vendor advisory confirms the fix in 1.152.1, applying this official update fully mitigates the issue. No additional mitigations are specified or required.
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
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) affecting versions before 1.152.1. In federated rooms, malicious homeservers could send specially crafted room events that interfere with Synapse's ability to serve full room history to clients using pagination. This improper input validation (CWE-20) causes clients to miss parts of the room history. The vulnerability has a CVSS 4.0 base score of 5.1 (medium severity) and was fixed in version 1.152.1.
Potential Impact
Clients connected to vulnerable Synapse servers may not receive the full history of federated rooms, potentially impacting user experience and completeness of chat history. There is no indication of data compromise or remote code execution. The impact is limited to incomplete room history display.
Mitigation Recommendations
Upgrade Synapse to version 1.152.1 or later, where this vulnerability is fixed. Since the vendor advisory confirms the fix in 1.152.1, applying this official update fully mitigates the issue. No additional mitigations are specified or required.
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: 5/28/2026, 4:48:44 PM
Last enriched: 5/28/2026, 5:04:59 PM
Last updated: 5/29/2026, 8:20:49 AM
Views: 8
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