What is CVE-2026-45056?

CVE-2026-45056 is Matrix Rust SDK: Sender-binding gaps in to-device and room-key attribution. The supplied enrichment data classifies it as Auth Bypass mapped to CWE-290 CWE-290.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Active exploitation is not confirmed from current sources for CVE-2026-45056. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-45056 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

3 public PoC repositories reported; 0 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS, identity provider logs, authentication audit logs where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-45056 using CVSS 6.9, EPSS 0%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

Workarounds are not confirmed from current sources. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

mediumAuth Bypasspublic exploit

CVE-2026-45056

CVE-2026-45056 — Matrix Rust SDK: Sender-binding gaps in to-device and room-key attribution

matrix-sdk-crypto is a no-network-IO implementation of a state machine that handles end-to-end encryption for Matrix clients. Starting in version 0.12.0 and prior to version 0.17.0, the matrix-sdk-crypto crate was missing a check for the user ID when decrypting an Olm-encrypted event containing the `sender_device_keys` property. This could be exploited to forge an encrypted to-device event, but only if the attacker colludes with the homeserver operator. This issue is fixed in matrix-sdk-crypto 0.17.0. There are no known workarounds for the issue.

Published Sep 11, 2026Updated Sep 11, 2026Sources: NVD, matrix-org (CNA), GitHub, GitHub Security Advisory, SOCRadar CTI

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Exploit code

public exploit, none observed

EPSS

ahead of 16% of scored CVEs

Affects

matrix-org

2 products listed

CVSS base

6.9

medium

Remediation

The vendor's own words where we have them.

Upgrade matrix-sdk-crypto to 0.16.1 or later (rust advisory GHSA-wfq4-36m3-9g42).

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
matrix-org	matrix-rust-sdk	>= 0.12.0, < 0.16.1	Vulnerable
rust	matrix-sdk-crypto	>= 0.12.0, < 0.16.1	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack Complexity

Low

Attack Vector

Network

Privileges Req

High

User Interaction

None

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
6.9	CVSS 4.0	medium	—	—	matrix-org (CNA)

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

What this weakness leads to

MITRE's own consequences and mitigations for the weakness class — the authority's wording, not guidance derived from the CVSS vector.

MITRE

CWE-290 · Authentication Bypass by Spoofing

Bypass Protection Mechanism
Gain Privileges or Assume Identity

Weakness & attack patterns

CWE-290

Attack patterns reported against this CVE. The ATT&CK techniques below are inferred from its weakness class.

CAPEC-21 · Exploitation of Trusted IdentifiersCAPEC-22 · Exploiting Trust in ClientCAPEC-459 · Creating a Rogue Certification Authority CertificateCAPEC-461 · Web Services API Signature Forgery Leveraging Hash Function Extension WeaknessCAPEC-473 · Signature SpoofCAPEC-476 · Signature Spoofing by MisrepresentationCAPEC-59 · Session Credential Falsification through PredictionCAPEC-60 · Reusing Session IDs (aka Session Replay)CAPEC-94 · Man in the Middle Attack

T1134Access Token Manipulation
T1528Steal Application Access Token
T1539Steal Web Session Cookie

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Repositories

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Prioritize edge telemetry for network-reachable matrix-rust-sdk, matrix-sdk-crypto.
Monitor for scanner or exploit-pattern traffic after 3 public PoC repositories were reported.

web/proxy/WAF logsapplication logsnetwork IDS/IPSidentity provider logsauthentication audit logs

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 6.9 (AV:N)
Sep 11, 2026 · NVD
Initial · CVE published
Sep 11, 2026 · NVD
CVE published by MITRE.
Sep 11, 2026 · SOCRadar CTI
Added · GHSA-wfq4-36m3-9g42 published (medium)
Jun 4, 2026 · GitHub Security Advisory

References

5 on the record

github.com/matrix-org/matrix-rust-sdk/pull/6553
Exploit, Third Party Advisory, Mitre
github.com/matrix-org/matrix-rust-sdk/releases/tag/matrix-sdk-0.16.1
Exploit, Third Party Advisory, Mitre
github.com/matrix-org/matrix-rust-sdk/security/advisories/GHSA-wfq4-36m3-9g42
Exploit, Third Party Advisory, Mitre
rustsec.org/advisories/RUSTSEC-2026-0159.html
Vendor Advisory, Mitre
github.com/advisories/GHSA-wfq4-36m3-9g42
Exploit, Third Party Advisory

Elsewhere on this site

matrix-orgevery CVE for this vendor
rustevery CVE for this vendor
Auth Bypasssame class
CWE-290other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-45056 is Matrix Rust SDK: Sender-binding gaps in to-device and room-key attribution, a medium vulnerability affecting matrix-rust-sdk, matrix-sdk-crypto from matrix-org, rust. The current evidence does not list it in CISA KEV, and the exploit status is: Active exploitation is not confirmed from current sources for CVE-2026-45056. Public exploit evidence is: 3 public PoC repositories reported; 0 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 6.9 describes technical severity, while EPSS 0% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.