CVE-2025-4896: Tenda AC10 Buffer Overflow Vulnerability

CVE-2025-4896 Overview

CVE-2025-4896 is a buffer overflow vulnerability affecting Tenda AC10 routers running firmware version 16.03.10.13. The flaw resides in the /goform/UserCongratulationsExec endpoint, where improper handling of the getuid argument allows attackers to overflow a fixed-size buffer. Remote attackers can trigger the condition over the network to corrupt memory on the device. The issue has been publicly disclosed, and exploit details are available through third-party vulnerability databases. The vulnerability maps to [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer) and [CWE-120] (Classic Buffer Overflow).

Critical Impact

Remote attackers with low-privileged access can corrupt memory on Tenda AC10 routers, leading to denial of service or potential arbitrary code execution on the device.

Affected Products

• Tenda AC10 router (hardware)
• Tenda AC10 firmware version 16.03.10.13
• Deployments exposing the router web management interface to untrusted networks

Discovery Timeline

• 2025-05-18 - CVE-2025-4896 published to NVD
• 2025-05-27 - Last updated in NVD database

Technical Details for CVE-2025-4896

Vulnerability Analysis

The vulnerability exists within the HTTP handler for /goform/UserCongratulationsExec in the Tenda AC10 web management interface. The handler accepts a user-supplied getuid parameter and processes it without enforcing length boundaries on the destination buffer. Supplying an oversized value causes adjacent memory to be overwritten, corrupting stack or heap structures used by the httpd service. Successful exploitation can crash the router or, depending on memory layout and protections, allow an attacker to redirect execution flow. The affected endpoint is reachable from the local network through the standard router management interface.

Root Cause

The root cause is the absence of bounds checking when copying the getuid argument into a fixed-size buffer. The firmware uses unsafe string handling routines typical of MIPS-based embedded Linux binaries, where functions like strcpy or sprintf operate on attacker-controlled input. Combined with the lack of stack canaries or address space layout randomization in many Tenda firmware builds, this creates conditions favorable for memory corruption attacks. The flaw is consistent with the patterns described in [CWE-120].

Attack Vector

An attacker sends a crafted HTTP request to the router's management interface targeting /goform/UserCongratulationsExec with an oversized getuid parameter. The attack requires network reachability to the management interface and low-privilege authenticated access. No user interaction is required to trigger the overflow. Technical write-up details are available in the GitHub CVE Documentation and the VulDB entry #309452.

No verified proof-of-concept code is reproduced here. Refer to the linked references for technical artifacts.

Detection Methods for CVE-2025-4896

Indicators of Compromise

• Unexpected reboots or crashes of the Tenda AC10 httpd service
• HTTP POST or GET requests to /goform/UserCongratulationsExec containing unusually long getuid parameter values
• Repeated malformed requests originating from a single internal or external host targeting the router management interface
• Loss of management interface availability following targeted HTTP traffic

Detection Strategies

• Inspect HTTP logs from the router or upstream network devices for requests to /goform/UserCongratulationsExec with parameter lengths exceeding normal bounds
• Deploy network intrusion detection signatures that flag long query strings or POST bodies sent to Tenda /goform/ endpoints
• Correlate router availability monitoring with HTTP traffic patterns to identify exploitation attempts that trigger denial of service

Monitoring Recommendations

• Capture and review traffic to TCP port 80 and 443 on the router management interface for anomalies
• Forward router syslog events to a centralized log platform and alert on httpd restarts or watchdog resets
• Restrict and monitor the source IP ranges permitted to access the management interface

How to Mitigate CVE-2025-4896

Immediate Actions Required

• Disable WAN-side access to the router management interface and restrict LAN-side access to trusted administrative hosts
• Change default and weak administrative credentials to reduce the pool of attackers able to reach the authenticated endpoint
• Segment the router management network from general user and guest networks
• Monitor the Tenda Official Website for firmware updates addressing this vulnerability

Patch Information

At the time of publication, no official vendor advisory or patched firmware release has been associated with CVE-2025-4896 in the NVD record. Administrators should track the VulDB CTI entry #309452 and Tenda support channels for updates. If the AC10 model has reached end-of-support, replacement with a currently maintained router is the recommended long-term remediation.

Workarounds

• Block external access to the router web administration interface using upstream firewall rules
• Place the router management VLAN behind an access control list that permits only specific administrator workstations
• If the device supports it, disable remote management features and require local console or VPN access for administration
• Consider replacing the affected device if firmware updates are not provided within an acceptable timeframe

# Example upstream ACL restricting management interface access
# (adapt to your firewall syntax)
iptables -A FORWARD -p tcp -d <router-ip> --dport 80 -s <admin-subnet> -j ACCEPT
iptables -A FORWARD -p tcp -d <router-ip> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <router-ip> --dport 443 -s <admin-subnet> -j ACCEPT
iptables -A FORWARD -p tcp -d <router-ip> --dport 443 -j DROP