How severe is CVE-2026-45056?

No CVSS score has been assigned to CVE-2026-45056 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-45056?

CVE-2026-45056 affects the following packages: matrix-sdk-crypto (crates.io). Ecosystems affected: crates.io.

How do I fix CVE-2026-45056?

Update matrix-sdk-crypto to 0.16.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-45056 is resolved across your whole dependency graph.

How do I detect CVE-2026-45056 in my crates.io dependencies?

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

How do I mitigate CVE-2026-45056 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-2026-45056 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-45056 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-2026-45056?

CVE-2026-45056 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 22th 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-2026-45056?

CVE-2026-45056 is classified as CWE-290 (CWE-290). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-45056 published, and has it been updated?

CVE-2026-45056 was published on September 11, 2026 and was last updated on October 2, 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-2026-45056 — matrix-sdk-crypto

Fix: matrix-org/matrix-rust-sdk#6553

CVE-2026-45056 is a CWE-290 vulnerability in matrix-sdk-crypto. A fix is available for matrix-sdk-crypto — see the affected versions and patch details below.

Matrix Rust SDK: Sender-binding gaps in to-device and room-key attribution

Also known asGHSA-wfq4-36m3-9g42RUSTSEC-2026-0159

Published

Sep 11, 2026

Updated

Oct 2, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

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-2026-45056.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs22th percentile — riskier than 22% 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-crypto

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

Impact

The matrix-sdk-crypto crate before 0.16.1 is missing a check for the sender's user ID when decrypting an Olm-encrypted to-device message containing the sender_device_keys property.

This could be exploited to spoof the sender of an encrypted to-device message, but only if the attacker colludes with (or is) the homeserver operator.

Patches

This issue is fixed in matrix-sdk-crypto 0.16.1.

Workarounds

There are no known workarounds for the issue.

References

This issue was fixed in https://github.com/matrix-org/matrix-rust-sdk/pull/6553.

For more information

If you have any questions or comments about this advisory, please email us at security at matrix.org.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🦀crates.io	`matrix-sdk-crypto`	≥ 0.12.0&&< 0.16.1	0.16.1`cargo update -p matrix-sdk-crypto --precise 0.16.1`

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-crypto, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update matrix-sdk-crypto to 0.16.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-45056 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

### Impact The `matrix-sdk-crypto` crate before 0.16.1 is missing a check for the sender's user ID when decrypting an Olm-encrypted to-device message containing the `sender_device_keys` property. This could be exploited to spoof the sender of an encrypted to-device message, but only if the attacker colludes with (or is) the homeserver operator. ### Patches This issue is fixed in `matrix-sdk-crypto` 0.16.1. ### Workarounds There are no known workarounds for the issue. ### References This issue was fixed in https://github.com/matrix-org/matrix-rust-sdk/pull/6553. ### For more informatio

O3 Security · Impact-Aware SCA

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