CVE-2026-45057 matrix-org CVE debrief

Who should care

Defenders responsible for systems using matrix-sdk-ui should assess exposure and apply the patch to prevent potential impersonation or spoofing. This includes verifying their inventory of affected systems, assessing exposure, and applying the patch to prevent potential impersonation or spoofing. Additionally, defenders should review compensating controls for exposed systems while remediation is scheduled and verified.

Why it matters

Defenders should prioritize verifying their inventory of affected systems, assessing exposure, and applying the patch to prevent potential impersonation or spoofing.

• Potential impersonation or spoofing of messages
• Increased risk for malicious homeserver administrators
• Need for verification of affected systems and patch application

Technical summary

The message edit validation logic in the matrix-sdk-ui crate before 0.16.1 is missing a check: when replacing an encrypted event, the replacement event itself is not required to be encrypted. This enables a malicious homeserver administrator (or an actor with equivalent power) to impersonate or spoof messages as if they were sent by a victim user. The vulnerability is caused by a missing check in the message edit validation logic, which allows for potential impersonation or spoofing of messages. Defenders should prioritize verifying their inventory of affected systems, assessing exposure, and applying the patch to prevent potential impersonation or spoofing.

Defensive priority

Defenders should prioritize verifying their inventory of affected systems, assessing exposure, and applying the patch to prevent potential impersonation or spoofing.

Recommended defensive actions

• Verify inventory of systems using matrix-sdk-ui
• Assess exposure to potential impersonation or spoofing
• Apply patch to matrix-sdk-ui (version 0.16.1 or later)
• Monitor for suspicious activity
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The source item from osv_dev provides details on the vulnerability in matrix-sdk-ui, including the missing check in the message edit validation logic. The source details are limited, so defenders should verify the affected systems and patch application to prevent potential impersonation or spoofing. The vulnerability has been reported and verified through source-provided information.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.