CVE-2026-5550: Tenda AC10 Buffer Overflow Vulnerability

CVE-2026-5550 Overview

CVE-2026-5550 is a stack-based buffer overflow vulnerability in the Tenda AC10 router running firmware version 16.03.10.10_multi_TDE01. The flaw resides in the fromSysToolChangePwd function within the /bin/httpd binary that serves the device's web management interface. Attackers can trigger the overflow remotely over the network by manipulating crafted input to the affected endpoint. Multiple endpoints in the HTTP daemon may be affected by the same underlying weakness [CWE-119]. Successful exploitation can lead to memory corruption, denial of service, and potentially arbitrary code execution on the embedded device.

Critical Impact

Authenticated network attackers can corrupt the httpd process stack on Tenda AC10 routers, potentially gaining control of the device and pivoting into the internal network.

Affected Products

• Tenda AC10 router (hardware revision 4.0)
• Tenda AC10 firmware 16.03.10.10_multi_TDE01
• /bin/httpd web management service on the affected firmware

Discovery Timeline

• 2026-04-05 - CVE-2026-5550 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-5550

Vulnerability Analysis

The vulnerability is a classic stack-based buffer overflow [CWE-119] in the fromSysToolChangePwd handler exposed by the Tenda AC10 web administration daemon. The handler processes password-change requests submitted to the router's HTTP interface and copies attacker-controlled parameter values into fixed-size stack buffers without validating their length. Because the overflow occurs on the call stack, an attacker who controls the overflowing data can overwrite the saved return address and adjacent local variables. According to the public finding, the same unsafe pattern is reached by 229 callers of an internal getValue-style helper, indicating the root cause likely extends across multiple HTTP endpoints in /bin/httpd.

Root Cause

The httpd binary uses unbounded string copy operations when extracting POST and query parameters from incoming requests. The fromSysToolChangePwd function does not enforce length limits before writing user-supplied data into stack-allocated buffers. The MIPS-based firmware on the AC10 does not consistently apply stack canaries or address-space layout randomization, which reduces the difficulty of converting the overflow into reliable code execution.

Attack Vector

Exploitation requires network access to the router's web management interface and low-privileged authentication to reach the fromSysToolChangePwd endpoint. An attacker submits an HTTP request containing an oversized value for one of the password-change parameters. The malformed payload overruns the destination buffer in the httpd worker, crashing the service or redirecting execution. Routers that expose the management interface to the WAN or to untrusted LAN segments face the highest risk. Refer to the GitHub Vulnerability Findings and VulDB #355314 for additional technical context.

Detection Methods for CVE-2026-5550

Indicators of Compromise

• Unexpected restarts or crashes of the httpd process on Tenda AC10 routers, often visible as gaps in the device's web UI availability.
• HTTP POST requests targeting the password-change endpoint containing abnormally long parameter values or non-printable bytes.
• Outbound connections from the router to unknown hosts following administrative requests, indicating possible post-exploitation activity.

Detection Strategies

• Inspect HTTP traffic to the router management interface for requests invoking fromSysToolChangePwd with parameter lengths that exceed expected bounds.
• Correlate router reboot events and httpd segmentation faults with preceding authenticated HTTP sessions from unusual source addresses.
• Apply network IDS signatures that flag oversized form fields in requests to Tenda administrative URLs.

Monitoring Recommendations

• Forward router syslog and crash telemetry to a centralized logging platform and alert on repeated httpd failures.
• Monitor administrative authentication events on the router and flag access from outside trusted management subnets.
• Track DNS and outbound traffic originating from the router itself to identify command-and-control activity following compromise.

How to Mitigate CVE-2026-5550

Immediate Actions Required

• Restrict access to the router's web administration interface to a trusted management VLAN and disable any WAN-side management exposure.
• Rotate router administrator credentials and disable unused accounts to reduce the pool of identities able to reach the vulnerable endpoint.
• Inventory Tenda AC10 devices running firmware 16.03.10.10_multi_TDE01 and prioritize them for replacement or firmware updates.

Patch Information

At the time of publication, no fixed firmware version is referenced in the NVD entry or the linked advisory. Consult the Tenda Official Site for updated firmware releases and monitor the GitHub Vulnerability Findings repository for vendor responses.

Workarounds

• Disable remote management on the WAN interface and limit LAN-side management to specific administrator hosts via firewall rules.
• Place the router's management interface behind a VPN so the HTTP daemon is not directly reachable from general user networks.
• If the device is end-of-life or no patched firmware is available, replace the affected AC10 routers with supported hardware that receives security updates.