VulnerabilityPublished 20 Nov 2025

CVE-2025-65220: Tenda AC21 router firmware · CVE-2025-65220 is a medium severity buffer overflow

Source CVE Database V5

Not known to be exploited · CVSS 4.3 Medium.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

4.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 18% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Attack Vector: Adjacent
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Adjacent: The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 20 Nov 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

AI-suggested

Network Segmentation: Isolate router management interfaces from general user networks to prevent unauthorized access from adjacent devices.
Access Control: Restrict access to the router’s management interface to trusted IP addresses or VLANs.
Disable Remote Management: Ensure that remote management over WAN is disabled unless absolutely necessary and secured via VPN or other strong authentication methods.
Monitor Network Traffic: Implement monitoring to detect unusual or malformed requests targeting /goform/SetVirtualServerCfg or other router endpoints.
Firmware Updates: Regularly check for firmware updates from Tenda and apply patches promptly once available.
Device Replacement: Consider replacing Tenda AC21 routers with devices from vendors with more robust security update policies if patching is delayed.
Incident Response: Prepare to respond to potential denial of service incidents by having backup connectivity options and procedures for rapid device reboot or replacement.
User Awareness: Educate users about the risks of connecting untrusted devices to the local network that could be used to exploit this vulnerability.

Description

CVE-2025-65220 is a medium severity buffer overflow vulnerability in the Tenda AC21 router firmware version V16.03.08.16, specifically in the /goform/SetVirtualServerCfg endpoint via the list parameter. The vulnerability can be exploited remotely without authentication or user interaction, but requires adjacent network access (AV:A). It impacts availability by potentially causing device crashes or reboots. There are no known exploits in the wild and no patches currently available. European organizations using Tenda AC21 routers, especially in home or small office environments, may be affected. Mitigation involves network segmentation, restricting access to router management interfaces, and monitoring for unusual device behavior. Countries with higher consumer adoption of Tenda networking equipment, such as Germany, France, and the UK, are more likely to be impacted.

Impact

For European organizations, the primary impact of CVE-2025-65220 is on availability. A successful exploit could cause Tenda AC21 routers to crash or reboot, leading to network downtime and disruption of internet connectivity. This can affect both home users and small businesses relying on these routers for critical connectivity. While the vulnerability does not compromise confidentiality or integrity, denial of service conditions can interrupt business operations, remote work, and access to cloud services. Organizations with remote or hybrid workforces may experience productivity losses if affected routers are used in home offices. Additionally, if the router is part of a larger network infrastructure, repeated crashes could complicate network management and incident response. The requirement for adjacent network access limits exploitation to attackers who have gained some level of internal network presence, such as malicious insiders or compromised devices within the local network. This reduces the risk of wide-scale remote exploitation but highlights the importance of internal network security controls. The lack of known exploits in the wild currently reduces immediate risk but does not preclude future exploitation attempts once details become more widely known.

Summary

CVE-2025-65220 identifies a buffer overflow vulnerability in the Tenda AC21 router firmware version V16.03.08.16. The flaw exists in the /goform/SetVirtualServerCfg endpoint, specifically in the handling of the 'list' parameter. Buffer overflow vulnerabilities occur when input data exceeds the allocated buffer size, potentially overwriting adjacent memory. This can lead to unpredictable behavior including crashes, reboots, or in some cases, arbitrary code execution. However, this particular vulnerability has a CVSS score of 4.3 (medium) with the vector indicating that the attack vector is adjacent network (AV:A), meaning the attacker must have access to the same local or adjacent network segment. No privileges are required (PR:N), no user interaction is needed (UI:N), and the impact is limited to availability (A:L) with no confidentiality or integrity impact. The vulnerability is categorized under CWE-121 (Stack-based Buffer Overflow). There are currently no known exploits in the wild and no patches have been published. The lack of authentication requirement means that an attacker on the local network could send crafted requests to the vulnerable endpoint to trigger the overflow, potentially causing denial of service by crashing the router or causing it to reboot. The absence of known exploits and patches suggests this is a newly disclosed vulnerability requiring attention from network administrators using this device. Given the nature of the vulnerability, exploitation is limited to attackers with local network access, reducing the risk from remote internet-based attackers unless the device management interface is exposed externally.

CWE-121Stack-based Buffer Overflow (opens in a new tab)
Variant weaknessLikelihood of exploit: HighCWE Top 25 (2025): #14
A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).
Operation · Build and Compilation · Environment Hardening
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index…
Architecture and Design
Use an abstraction library to abstract away risky APIs. Not a complete solution.
Implementation
Implement and perform bounds checking on input.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/Madgeaaaaa/MY_VULN_2/blob/main/Tenda/VULN1.md (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 27 Nov 2025, 15:49 UTC

WeaknessesCWE-121

Technical details

References

Community reviews

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