CVE-2026-45056: Matrix Rust SDK Sender-binding Gaps Vulnerability

MODERATE
Advisory Identifier: GHSA-wfq4-36m3-9g42
Share
CWE-290
Published
Advisory Summary

CVE-2026-45056 is a MODERATE sender-binding gaps vulnerability (CWE-290: Authentication Bypass by Spoofing) affecting Matrix Rust SDK libraries in the crates.io ecosystem. The issue involves sender-binding gaps in to-device and room-key attribution. Remediation is available by upgrading affected packages to version 0.16.1.

CVE-2026-45056 at a Glance

CVE Identifier CVE-2026-45056
GHSA Identifier GHSA-wfq4-36m3-9g42
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-290: Authentication Bypass by Spoofing
Affected Product Matrix Rust SDK
Package Ecosystem crates.io
Published Date
Last Updated

How to Fix CVE-2026-45056

To remediate this vulnerability, upgrade all affected Matrix Rust SDK dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

matrix-sdk-crypto fixed: 0.16.1 
Upgrade matrix-sdk-crypto to 0.16.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for matrix-sdk-crypto

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-45056, inspect your project dependencies for Matrix Rust SDK:

inspect dependencies for matrix-sdk-crypto

Analyze the terminal output to locate any version of Matrix Rust SDK in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.16.1), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-290: Authentication Bypass by Spoofing, where this attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks. In Matrix Rust SDK, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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](mailto:security@matrix.org).

CVE-2026-45056 Affected Matrix Rust SDK Versions

1 component(s)
Fixed Versions:
0.16.1
Product / Package Ecosystem Affected Versions Fixed Version
matrix-sdk-crypto
 crates.io
≥ 0.12.0
< 0.16.1
0.16.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/matrix-org/matrix-rust-sdk/security/advisories/GHSA-wfq4-36m3-9g42
Matrix Rust SDK Source Repository REPOSITORY
https://github.com/matrix-org/matrix-rust-sdk/pull/6553
Matrix Rust SDK Source Repository REPOSITORY
https://github.com/matrix-org/matrix-rust-sdk
Matrix Rust SDK Release RELEASE
https://github.com/matrix-org/matrix-rust-sdk/releases/tag/matrix-sdk-0.16.1
rustsec.org/advisories/rustsec-... WEB
https://rustsec.org/advisories/RUSTSEC-2026-0159.html

Frequently Asked Questions

What is CVE-2026-45056?
CVE-2026-45056 is a security vulnerability in Matrix Rust SDK involving Sender-binding gaps in to-device and room-key attribution under CWE-290: Authentication Bypass by Spoofing.
Which Matrix Rust SDK versions are affected?
Affected versions include releases prior to 0.16.1 across affected packages: matrix-sdk-crypto.
What version fixes CVE-2026-45056?
Upgrading to 0.16.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is matrix-sdk-crypto affected?
Yes, matrix-sdk-crypto is affected in releases prior to 0.16.1. Upgrade your dependency to 0.16.1 or later.
What CWE is associated with CVE-2026-45056?
CVE-2026-45056 is classified under CWE-290: Authentication Bypass by Spoofing (This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.).
How can I check crates.io dependencies for CVE-2026-45056?
Run the dependency tree command: 'inspect dependencies for matrix-sdk-crypto'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-wfq4-36m3-9g42",
  "modified" : "2026-06-04T14:47:05Z",
  "published" : "2026-06-04T14:47:05Z",
  "aliases" : [ "CVE-2026-45056" ],
  "summary" : "Matrix Rust SDK: Sender-binding gaps in to-device and room-key attribution",
  "details" : "### Impact\n\nThe `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.\n\nThis 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.\n\n### Patches\n\nThis issue is fixed in `matrix-sdk-crypto` 0.16.1.\n\n### Workarounds\n\nThere are no known workarounds for the issue.\n\n### References\n\nThis issue was fixed in https://github.com/matrix-org/matrix-rust-sdk/pull/6553.\n\n### For more information\n\nIf you have any questions or comments about this advisory, please email us at [security at matrix.org](mailto:security@matrix.org).",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "matrix-sdk-crypto"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.12.0"
      }, {
        "fixed" : "0.16.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/matrix-org/matrix-rust-sdk/security/advisories/GHSA-wfq4-36m3-9g42"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/matrix-org/matrix-rust-sdk/pull/6553"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/matrix-org/matrix-rust-sdk"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/matrix-org/matrix-rust-sdk/releases/tag/matrix-sdk-0.16.1"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2026-0159.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-290" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-04T14:47:05Z",
    "nvd_published_at" : null
  }
}