CVE-2026-2930: Tenda A18 Buffer Overflow Vulnerability

CVE-2026-2930 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda A18 wireless router firmware version 15.13.07.13. The vulnerability exists within the webCgiGetUploadFile function located in the /cgi-bin/UploadCfg file of the Httpd Service component. By manipulating the boundary argument, an attacker can trigger a stack-based buffer overflow condition. This vulnerability can be exploited remotely over the network, and exploit information has been made publicly available.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially compromise the integrity, confidentiality, and availability of affected Tenda A18 routers. The network-accessible attack vector makes this vulnerability particularly dangerous for exposed devices.

Affected Products

• Tenda A18 Firmware version 15.13.07.13
• Tenda A18 Hardware Device

Discovery Timeline

• 2026-02-22 - CVE-2026-2930 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2026-2930

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), which encompasses memory corruption issues arising from inadequate boundary checking. The vulnerable code resides in the Httpd Service, specifically within the configuration upload functionality.

The webCgiGetUploadFile function processes HTTP multipart form data for configuration file uploads. When parsing the boundary parameter from incoming requests, the function fails to properly validate the length of user-supplied input before copying it to a stack-based buffer. This oversight allows attackers to provide an oversized boundary string that exceeds the allocated buffer space, overwriting adjacent stack memory.

The network-accessible nature of this vulnerability significantly increases its risk profile, as attackers can exploit it remotely without requiring physical access to the device or prior authentication. This makes any internet-exposed Tenda A18 devices particularly vulnerable.

Root Cause

The root cause of CVE-2026-2930 is insufficient input validation within the webCgiGetUploadFile function. The function does not enforce proper bounds checking when handling the boundary argument from HTTP multipart requests. When processing configuration upload requests at the /cgi-bin/UploadCfg endpoint, the boundary parameter value is copied to a fixed-size stack buffer without verifying that the input length does not exceed the buffer capacity. This classic stack-based buffer overflow pattern allows stack corruption when an attacker supplies a maliciously crafted boundary string.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An attacker can craft a malicious HTTP POST request targeting the /cgi-bin/UploadCfg endpoint with a specially crafted multipart form data boundary parameter. The oversized boundary string triggers the buffer overflow in the webCgiGetUploadFile function.

The vulnerability mechanism involves the following sequence:

1. An attacker sends an HTTP POST request to the vulnerable /cgi-bin/UploadCfg endpoint
2. The request contains a multipart form-data content type with a manipulated boundary parameter
3. The webCgiGetUploadFile function processes this request and copies the boundary value to a stack buffer
4. Due to insufficient bounds checking, an oversized boundary value overwrites adjacent stack memory
5. This can lead to control flow hijacking, denial of service, or arbitrary code execution

For detailed technical analysis and proof-of-concept information, refer to the GitHub Issue Report and VulDB entry.

Detection Methods for CVE-2026-2930

Indicators of Compromise

• Unusual HTTP POST requests to /cgi-bin/UploadCfg with abnormally long boundary parameters in the Content-Type header
• Unexpected router crashes or reboots that may indicate exploitation attempts causing denial of service
• Anomalous outbound network connections from the router following exploitation
• Configuration changes on the device that were not authorized by administrators

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests to /cgi-bin/UploadCfg with boundary parameters exceeding normal lengths
• Deploy web application firewall (WAF) rules to block multipart form-data requests with oversized boundary values
• Monitor Httpd Service logs on Tenda A18 devices for unusual access patterns to the configuration upload endpoint
• Utilize SentinelOne Singularity to detect anomalous behavior patterns indicative of buffer overflow exploitation

Monitoring Recommendations

• Enable comprehensive logging on network perimeter devices to capture all traffic destined for Tenda A18 management interfaces
• Implement alerting for any access attempts to /cgi-bin/UploadCfg from untrusted network segments
• Regularly review router logs for signs of repeated failed exploitation attempts or denial of service conditions
• Monitor for firmware integrity changes that could indicate successful compromise

How to Mitigate CVE-2026-2930

Immediate Actions Required

• Restrict network access to the router's web management interface to trusted internal networks only
• Implement firewall rules to block external access to the Httpd Service on affected Tenda A18 devices
• Disable remote management features if not required for business operations
• Segment IoT and network infrastructure devices from critical business networks

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Organizations should monitor the Tenda Official Website for firmware updates addressing CVE-2026-2930. Until a patch is available, implementing the workarounds and network-level mitigations described below is critical to reducing exposure risk.

For additional vulnerability intelligence, reference the VulDB entry for updates on patch availability.

Workarounds

• Place affected Tenda A18 devices behind a firewall and restrict access to the management interface to specific trusted IP addresses
• Disable the web-based management interface if alternative management methods are available
• Implement network segmentation to isolate vulnerable devices from sensitive network segments
• Consider replacing vulnerable devices with alternative products if patches are not made available in a timely manner

# Example: Restrict access to router management interface using iptables on upstream firewall
# Block external access to HTTP management port (typically 80 or 8080)
iptables -A FORWARD -d <TENDA_A18_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <TENDA_A18_IP> -p tcp --dport 8080 -j DROP

# Allow only trusted management subnet
iptables -I FORWARD -s 192.168.1.0/24 -d <TENDA_A18_IP> -p tcp --dport 80 -j ACCEPT