CVE-2025-31355 is a vulnerability identified in the firmware signature validation mechanism of the Tenda AC6 V5.0 router, specifically in firmware version V02.03.01.110. The core issue relates to CWE-494, which involves downloading code without proper integrity checks. In this case, the router’s firmware update process fails to adequately verify the authenticity and integrity of the firmware image or update files. An attacker who can supply a maliciously crafted file—likely through administrative or privileged access—can exploit this flaw to execute arbitrary code on the device. This could allow the attacker to alter router configurations, intercept or redirect network traffic, or use the device as a foothold for further network compromise. The CVSS 3.1 score of 7.2 reflects high severity, with network attack vector (AV:N), low attack complexity (AC:L), but requiring high privileges (PR:H), no user interaction (UI:N), and impacting confidentiality, integrity, and availability (C:H/I:H/A:H). Although no public exploits are currently known, the vulnerability’s nature and impact make it a critical concern for network security. The lack of a patch at the time of reporting increases urgency for interim mitigations.

For European organizations, exploitation of this vulnerability could lead to severe consequences including unauthorized control over network routing devices, interception of sensitive communications, and disruption of network services. This can compromise confidential data, degrade service availability, and undermine trust in network infrastructure. Critical sectors such as finance, healthcare, government, and telecommunications that rely on secure and stable network equipment are particularly vulnerable. The ability to execute arbitrary code on routers can facilitate lateral movement within networks, enabling attackers to escalate attacks or deploy ransomware. Given the widespread use of Tenda routers in small to medium enterprises and some consumer environments across Europe, the potential impact spans from localized business disruptions to broader supply chain risks if compromised devices are used as attack vectors.

1. Immediately restrict administrative access to the Tenda AC6 V5.0 routers by limiting management interfaces to trusted networks and using strong authentication methods. 2. Monitor network traffic and device logs for unusual firmware update attempts or unauthorized file uploads. 3. Disable remote firmware update capabilities if not strictly necessary or restrict them to secure channels and authenticated sessions. 4. Implement network segmentation to isolate vulnerable devices from critical infrastructure and sensitive data. 5. Engage with Tenda support channels to obtain official patches or firmware updates addressing this vulnerability as soon as they become available. 6. If patching is delayed, consider replacing affected devices with alternative hardware that has verified secure update mechanisms. 7. Conduct regular security audits and vulnerability assessments on network devices to detect and remediate similar issues proactively.