How severe is CVE-2025-66622?

No CVSS score has been assigned to CVE-2025-66622 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2025-66622?

CVE-2025-66622 affects the following packages: matrix-sdk-base (crates.io). Ecosystems affected: crates.io.

How do I fix CVE-2025-66622?

Update matrix-sdk-base to 0.16.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66622 is resolved across your whole dependency graph.

How do I detect CVE-2025-66622 in my crates.io dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for matrix-sdk-base, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2025-66622 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2025-66622 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-66622 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2025-66622?

CVE-2025-66622 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 39th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2025-66622?

CVE-2025-66622 is classified as CWE-755 (CWE-755). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2025-66622 published, and has it been updated?

CVE-2025-66622 was published on December 9, 2025 and was last updated on November 4, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🦀 crates.io

Not in CISA KEV

CVE-2025-66622 — matrix-sdk-base

Fix: matrix-org/matrix-rust-sdk@4ea0418

CVE-2025-66622 is a CWE-755 vulnerability in matrix-sdk-base. A fix is available for matrix-sdk-base — see the affected versions and patch details below.

matrix-sdk-base is vulnerable to DoS via custom m.room.join_rules event values

Also known asGHSA-jj6p-3m75-g2p3RUSTSEC-2025-0135

Published

Dec 9, 2025

Updated

Nov 4, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-66622.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk+0.03%

Lower risk than most CVEs39th percentile — riskier than 39% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🦀matrix-sdk-base

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.

Description

The matrix-sdk-base crate is unable to handle responses that include custom m.room.join_rules values due to a serialization bug.

This can be exploited to cause a denial-of-service condition, if a user is invited to a room with non-standard join rules, the crate's sync process will stall, preventing further processing for all rooms.

Patches

The issue is fixed in matrix-sdk-base 0.16.0.

Workarounds

Users can leave affected rooms on another client to mitigate the issue.

References

The issue was fixed in https://github.com/matrix-org/matrix-rust-sdk/pull/5924.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🦀crates.io	`matrix-sdk-base`	all versions	0.16.0`cargo update -p matrix-sdk-base --precise 0.16.0`

Affected Products

1 product · 1 configurations

Application

matrix-rust-sdkmatrix

< 0.16.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for matrix-sdk-base, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update matrix-sdk-base to 0.16.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66622 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

The matrix-sdk-base crate is unable to handle responses that include custom m.room.join_rules values due to a serialization bug. This can be exploited to cause a denial-of-service condition, if a user is invited to a room with non-standard join rules, the crate's sync process will stall, preventing further processing for all rooms. ### Patches The issue is fixed in matrix-sdk-base 0.16.0. ### Workarounds Users can leave affected rooms on another client to mitigate the issue. ### References The issue was fixed in https://github.com/matrix-org/matrix-rust-sdk/pull/5924.

O3 Security · Impact-Aware SCA

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