CVE-2025-31355 is a High severity (CVSS 7.2) flaw in the firmware update function of the Tenda AC6 router, version V5.0 V02.03.01.110. A crafted file can lead to code execution. The record gives no fixed version, so check Tenda's support site and limit access to the admin page.
What's affected
The record names the Tenda AC6 router, hardware version V5.0, with firmware V02.03.01.110. The description says the firmware signature validation functionality can be abused: a specially crafted malicious file can lead to arbitrary code execution, and an attacker can provide such a file to trigger the issue.
The weakness is CWE-494, download of code without integrity check. The vector is CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H. A privileges required value of High means the attacker is expected to need administrative access to the router, which narrows the exposure. The record does not mark the CVE as in CISA KEV.
The disclosure comes from Cisco Talos, report TALOS-2025-2161. This post could not read that page, so it does not describe any detail beyond the record. The record does not list a fixed firmware version. Do not assume a later firmware fixes this until Tenda or Talos says so.
How to check if you're exposed
Log in to the router's admin page from inside your network and read the firmware version under the system status or system settings screen. A match to V02.03.01.110 on an AC6 V5.0 is in scope.
Next, check whether the admin interface is reachable from outside your network. From a device that is not on your home or office network, try to open the router's public address on its admin port. If you can reach the login page, remote administration is on. Turn it off.
Also check who knows the admin password. If the router still uses the default password, or one reused elsewhere, change it now. The attack in this record requires administrative access, so the strength of that password is your main protection.
Finally, look at Tenda's support page for the AC6 to see whether a newer firmware is listed and what its release notes say.
What to do now
- Check the firmware version on every Tenda AC6 V5.0 you manage.
- Turn off remote administration and make sure the admin page is only reachable from the trusted LAN.
- Change the admin password to a strong, unique one.
- Look for a newer firmware on Tenda's official support site and read its notes. Only download firmware from the vendor's own site.
- If the router sits in a place where you cannot trust the local network, consider replacing it with a model that still receives security updates.
Why it matters
Routers and other embedded devices update their firmware from a file uploaded by an administrator. A signature check is what keeps a modified file from being accepted. When that check is weak or can be bypassed, a crafted file can install attacker controlled code that runs with the device's full privileges. The weakness class is CWE-494: code is accepted without a reliable integrity check.
Such devices are hard to monitor and rarely run endpoint protection, so a compromised router can sit unnoticed for a long time while it sees all traffic that passes through it. That is why the practical defenses are about reducing who can reach the update function: no remote administration, strong credentials, and firmware from the vendor only. Where a vendor stops shipping fixes, replacement is the only complete answer.
Quick check
Does an attacker need my admin password?
The CVSS vector lists privileges required as High, which points to administrative access. The record does not say more, so protect the admin account and interface.
Is there a fixed firmware?
The record does not name one. Check Tenda's support site and the Talos report, and do not assume newer firmware is fixed without a statement.
Sources
Last reviewed: 19 October 2026.
