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CVE-2026-45056

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

6.9 MediumFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
High
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
High
Availability
None

Exploit likelihood

0.31%Up 0.3 points since Jun 12, 2026
90%50%10%1%

What each source reports

CVE List Score used 6.9

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.

Record
CVE-2026-45056
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-290
Updated
2026-11-02
EUVDEUVD-2026-76763 6.9

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.

Record
EUVD-2026-76763
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-wfq4-36m3-9g42 6.9

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

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.

Record
GHSA-wfq4-36m3-9g42
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-290
Updated
2026-11-02
NVD 6.9

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.

Record
CVE-2026-45056
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Weakness
CWE-290
Updated
2026-11-02
OSV 6.9

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.

Record
CVE-2026-45056
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-290
Updated
2026-11-04
OSVGHSA-wfq4-36m3-9g42 6.9

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

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.

Record
GHSA-wfq4-36m3-9g42
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-290
Updated
2026-11-02
OSVRUSTSEC-2026-0159 No score

Sender-binding gaps in to-device messages

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.

Record
RUSTSEC-2026-0159
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
matrix-sdk-crypto
crates.io
 0.12.0 up to 0.16.1
0.16.1

History

History
RecordedChangedSources
factsOSV
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-45056 is a medium vulnerability (CVSS 6.9) in Matrix-org Matrix-rust-sdk, published June 3, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.31%, the 23rd percentile. Fixed in matrix-sdk-crypto 0.16.1.

References

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