Critical Buffer Overflow Vulnerability in Tenda W12 and i24 Routers (CVE-2025-3820)

A newly disclosed critical vulnerability (CVE-2025-3820) affecting Tenda W12 and i24 routers allows remote attackers to execute arbitrary code through a stack-based buffer overflow. The flaw resides in the cgiSysUplinkCheckSet function of the router’s HTTP daemon and can be triggered by manipulating hostIp1 or hostIp2 parameters. With a CVSS v3.1 score of 8.8 (High), this vulnerability poses significant risk to networks using affected devices.

Technical Analysis

The vulnerability occurs in firmware versions 3.0.0.4(2887) and 3.0.0.5(3644) of both Tenda W12 and i24 router models. Attackers can exploit the flaw remotely without authentication by sending specially crafted requests to the vulnerable HTTP daemon component. The buffer overflow occurs when processing overly long strings in the hostIp1 or hostIp2 parameters passed to the cgiSysUplinkCheckSet function located in /bin/httpd.

According to VulDB and NVD records, successful exploitation could lead to complete system compromise, allowing attackers to bypass security controls, install malware, or pivot to other network devices. A proof-of-concept exploit has been publicly disclosed on GitHub, increasing the likelihood of active exploitation attempts.

CVSS Scoring and Impact

The vulnerability has been assessed under multiple CVSS versions, with consistent high-severity ratings across all metrics:

CVSS Version	Base Score	Vector String
v4.0	8.7 (High)	AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
v3.1	8.8 (High)	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
v2.0	9.0 (High)	AV:N/AC:L/Au:S/C:C/I:C/A:C

The vulnerability shares similarities with CVE-2025-3802, another buffer overflow affecting Tenda routers, suggesting potential systemic issues in the vendor’s codebase. The EPSS (Exploit Prediction Scoring System) currently estimates a 0.05% probability of active exploitation within the next 30 days.

Detection and Mitigation

Organizations using affected Tenda router models should immediately implement the following measures:

Disable remote management features on all affected devices
Monitor network traffic for unusual HTTP requests targeting the /bin/httpd service
Check for firmware updates on Tenda’s official support portal
Consider replacing affected devices if no security patch becomes available

Network monitoring solutions should be configured to alert on HTTP requests containing unusually long strings in the hostIp1 or hostIp2 parameters. IDS/IPS rules can be implemented to block known exploit patterns based on the public PoC.

Conclusion

CVE-2025-3820 represents a serious threat to networks utilizing vulnerable Tenda router models. The public availability of exploit code combined with the high CVSS score makes prompt mitigation essential. Organizations should prioritize identifying affected devices in their inventory and implementing compensating controls until an official patch becomes available.

The vulnerability highlights the ongoing risks associated with network edge devices and the importance of maintaining current firmware versions. This case also demonstrates how buffer overflow vulnerabilities continue to persist in embedded systems despite being a well-understood attack vector.