CVE-2025-66622Network attack vector

Sync processing stall via custom join-rule serialization

Published Dec 9, 2025 · Updated Dec 9, 2025

Denial of service in matrix-rust-sdk before 0.16.0 allows remote attackers to stall all room sync via a crafted join-rule event. BaseRoomInfo converts custom m.room.join_rules variants into RoomInfo even though Ruma cannot safely reserialize variants with unknown associated data. A victim must receive a room invitation or sync event using a nonstandard join rule; processing then stops for every room until the affected room is left through another client.

CVSS severity7.5
High
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in matrix-rust-sdk before 0.16.0 allows remote attackers to stall all room sync via a crafted join-rule event. BaseRoomInfo converts custom m.room.join_rules variants into RoomInfo even though Ruma cannot safely reserialize variants with unknown associated data. A victim must receive a room invitation or sync event using a nonstandard join rule; processing then stops for every room until the affected room is left through another client.

The record

CVE
CVE-2025-66622
Published
Dec 9, 2025
Updated
Dec 9, 2025
Vendor
The Matrix.org Foundation
Product
matrix-rust-sdk
Classifications
CWE-755, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 9, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 9, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.16.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Matrix.org Foundation · matrix-rust-sdkversion=< 0.16.0

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
1.3GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-755Improper Handling of Exceptional Conditions
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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