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matrix-sdk-crypto vulnerable to sender of encrypted events being spoofed by homeserver administrator

Moderate severity GitHub Reviewed Published Jun 10, 2025 in matrix-org/matrix-rust-sdk • Updated Jun 12, 2025

Package

cargo matrix-sdk-crypto (Rust)

Affected versions

>= 0.8.0, < 0.11.1

Patched versions

0.11.1

Description

Summary

matrix-sdk-crypto since version 0.8.0 up to 0.11.0 does not correctly validate the sender of an encrypted event. Accordingly, a malicious homeserver operator can modify events served to clients, making those events appear to the recipient as if they were sent by another user.

Although the CVSS score is 4.9 (AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N), we consider this a High Severity security issue.

Details

The Matrix specification requires that clients ensure that "the event’s sender, room_id, and the recorded session_id match a trusted session". The vulnerable matrix-sdk-crypto versions check that the room_id matches that of the session denoted by session_id, but do not check the sender.

Patches

The issue is resolved by 13c1d20, included in versions 0.11.1 and 0.12.0 of matrix-sdk-crypto.

Workarounds

Since a successful attack requires administrator access to the homeserver, users who trust the administrators of their local homeserver are not affected.

References

References

@richvdh richvdh published to matrix-org/matrix-rust-sdk Jun 10, 2025
Published by the National Vulnerability Database Jun 10, 2025
Published to the GitHub Advisory Database Jun 10, 2025
Reviewed Jun 10, 2025
Last updated Jun 12, 2025

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
High
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(8th percentile)

Weaknesses

CVE ID

CVE-2025-48937

GHSA ID

GHSA-x958-rvg6-956w

Source code

Credits

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