Summary
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.
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.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
This issue is fixed in matrix-sdk-crypto 0.16.1.
Frequently Asked Questions
- What is CVE-2026-45056? CVE-2026-45056 is a medium-severity security vulnerability in matrix-sdk-crypto (rust), affecting versions >= 0.12.0, < 0.16.1. It is fixed in 0.16.1.
- Which versions of matrix-sdk-crypto are affected by CVE-2026-45056? matrix-sdk-crypto (rust) versions >= 0.12.0, < 0.16.1 is affected.
- Is there a fix for CVE-2026-45056? Yes. CVE-2026-45056 is fixed in 0.16.1. Upgrade to this version or later.
- Is CVE-2026-45056 exploitable, and should I be worried? Whether CVE-2026-45056 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-45056 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-45056? Upgrade
matrix-sdk-cryptoto 0.16.1 or later.