CVE-2025-67903: Mender Client Signature Bypass Vulnerability

CVE-2025-67903 Overview

CVE-2025-67903 is a cryptographic signature verification bypass affecting Northern.tech Mender Client 5 before version 5.0.4. Mender is an over-the-air (OTA) software update manager widely deployed across Linux-based embedded and Internet of Things (IoT) devices. The flaw allows an attacker to bypass signature verification on update artifacts, undermining the integrity guarantees that the update pipeline depends on. Because Mender is typically responsible for delivering trusted firmware and application updates to fleets of devices, a signature bypass can be leveraged to deploy unauthorized payloads. Operators relying on signed artifacts to gate production rollouts should treat this as a supply chain integrity issue.

Critical Impact
Attackers can deliver unsigned or maliciously modified update artifacts to Mender-managed devices, breaking the chain of trust for OTA updates.

Affected Products

Northern.tech Mender Client 5, all versions prior to 5.0.4
Linux-based embedded systems and IoT fleets using the affected Mender Client for OTA updates
Deployments depending on Mender artifact signature verification for update integrity

Discovery Timeline

2026-05-27 - CVE-2025-67903 published to the National Vulnerability Database (NVD)
2026-05-27 - Last updated in NVD database

Technical Details for CVE-2025-67903

Vulnerability Analysis

The vulnerability is a cryptographic signature verification bypass [CWE-347 class] in the Mender Client. The Mender Client downloads update artifacts and validates them against a configured public key before installing them on a device. When verification operates correctly, only artifacts signed by the holder of the corresponding private key are accepted. In affected releases of Mender Client 5, this verification path can be bypassed, allowing artifacts that should fail signature checks to be processed as if valid. The result is that the integrity boundary protecting OTA installations no longer holds.

Root Cause

Northern.tech has documented the issue in its Mender Blog CVE-2025-67903 Analysis. The defect resides in the artifact verification logic of the Mender Client 5 series and is corrected in 5.0.4. No public exploit, proof-of-concept, or CISA Known Exploited Vulnerabilities (KEV) listing is associated with this CVE at the time of publication.

Attack Vector

An attacker who can influence the update artifact delivered to a Mender-managed device — for example, through a compromised update server, a malicious mirror, or a network position enabling artifact substitution — can craft an artifact that bypasses signature validation. Once installed, the artifact executes with the privileges of the Mender update process, which on most deployments means root-level control of the device. This converts an integrity weakness into full device compromise without requiring access to the legitimate signing key.

No verified exploit code is publicly available. Refer to the vendor analysis for technical specifics on the verification flow and the conditions required to trigger the bypass.

Detection Methods for CVE-2025-67903

Indicators of Compromise

Mender Client deployments running any version of the 5.x series prior to 5.0.4
Successful artifact installations on managed devices that do not correspond to a known, signed release from the central Mender server
Unexpected changes to root filesystem partitions or /data/mender state files outside of scheduled deployment windows

Detection Strategies

Inventory all endpoints running mender or mender-client and compare installed versions against 5.0.4 or later
Cross-reference deployment logs on the Mender server with artifact installation events on devices to identify installs without a matching authorized deployment
Validate the public key configured in /etc/mender/mender.conf (ArtifactVerifyKey) on each device and alert on configuration drift

Monitoring Recommendations

Forward Mender Client logs (/var/log/mender or journalctl -u mender-client) to a centralized logging or SIEM platform for review of verify and install events
Monitor outbound connections from devices to the configured Mender server and alert on connections to unexpected update endpoints
Track artifact checksums on the server side and reconcile them against the artifacts actually installed on the fleet

How to Mitigate CVE-2025-67903

Immediate Actions Required

Upgrade all Mender Client 5 installations to version 5.0.4 or later as the primary remediation
Audit the update server, signing infrastructure, and artifact repositories for evidence of unauthorized artifacts produced or distributed before the upgrade
Rotate signing keys if there is any indication that unauthorized artifacts may have been delivered to production devices

Patch Information

Northern.tech has released Mender Client 5.0.4, which corrects the signature verification logic. Details of the fix are described in the Mender Blog CVE-2025-67903 Analysis. Additional product information is available on the Northern.tech homepage. Operators should plan a staged rollout of the fixed client across development, staging, and production fleets, validating that signature verification behaves correctly on a representative device before broad deployment.

Workarounds

Restrict network access so that Mender clients can reach only the authorized update server, reducing the opportunity for artifact substitution
Enforce mutual TLS between the Mender Client and the update server to limit attacker positioning on the network path
Pause automated deployments to production devices until the patched client is installed and verified

bash

# Verify installed Mender Client version on a managed device
mender --version

# Confirm the configured artifact verification key is present
grep -i ArtifactVerifyKey /etc/mender/mender.conf