CVE-2025-10838 Overview
CVE-2025-10838 is a buffer overflow vulnerability in the Tenda AC21 router running firmware version 16.03.08.16. The flaw resides in the function sub_45BB10 within the /goform/WifiExtraSet endpoint. Attackers can trigger the overflow by manipulating the wpapsk_crypto argument sent to the web management interface. The vulnerability is remotely exploitable and a public proof-of-concept has been released, increasing the likelihood of opportunistic exploitation against exposed devices. The underlying weakness is classified as [CWE-119] improper restriction of operations within the bounds of a memory buffer.
Critical Impact
Remote attackers with low-privilege access to the router web interface can corrupt memory through the wpapsk_crypto parameter, enabling potential arbitrary code execution on the device.
Affected Products
- Tenda AC21 router (hardware)
- Tenda AC21 firmware version 16.03.08.16
- Web management endpoint /goform/WifiExtraSet
Discovery Timeline
- 2025-09-23 - CVE-2025-10838 published to NVD
- 2025-10-03 - Last updated in NVD database
Technical Details for CVE-2025-10838
Vulnerability Analysis
The vulnerability is a stack or heap buffer overflow inside the sub_45BB10 function reached through the /goform/WifiExtraSet HTTP handler in the Tenda AC21 web server. The handler processes wireless configuration parameters submitted by an authenticated user. When the wpapsk_crypto parameter is supplied, the function copies attacker-controlled data into a fixed-size buffer without validating the input length. The resulting memory corruption can overwrite adjacent stack variables, saved return addresses, or heap metadata. Successful exploitation can crash the router, hijack control flow, or enable execution of attacker-supplied MIPS shellcode within the embedded Linux environment of the AC21.
Root Cause
The root cause is missing bounds checking on the wpapsk_crypto POST parameter before it is copied into an internal buffer inside sub_45BB10. The function trusts the size of the attacker-controlled string, which is characteristic of unsafe strcpy, sprintf, or memcpy patterns commonly seen in Tenda goform handlers.
Attack Vector
The attack vector is network-based. The attacker must reach the router HTTP interface and submit a crafted POST request to /goform/WifiExtraSet with an oversized wpapsk_crypto value. Low-privilege credentials are required, but routers with default credentials or exposed management interfaces lower this barrier significantly. No user interaction is required to trigger the overflow.
// Vulnerability mechanism (prose description - no synthetic exploit code)
// POST /goform/WifiExtraSet HTTP/1.1
// Body contains: wpapsk_crypto=<long attacker-controlled string>
// The handler sub_45BB10 copies wpapsk_crypto into a fixed-size buffer
// without length validation, corrupting adjacent memory.
See the GitHub PoC Repository for the published technical details.
Detection Methods for CVE-2025-10838
Indicators of Compromise
- Unexpected HTTP POST requests to /goform/WifiExtraSet containing unusually long wpapsk_crypto parameter values.
- Router web server (httpd) crashes, reboots, or watchdog resets correlated with inbound management requests.
- Outbound connections from the router to unknown hosts following management interface activity, suggesting post-exploitation staging.
Detection Strategies
- Inspect web traffic to router management interfaces for wpapsk_crypto parameters exceeding expected WPA pre-shared key lengths.
- Monitor for repeated authentication followed by malformed POSTs to /goform/ endpoints, a common Tenda exploitation pattern.
- Apply IDS/IPS signatures targeting CWE-119 buffer overflow patterns against Tenda goform URIs.
Monitoring Recommendations
- Log all administrative access to Tenda AC21 routers and forward logs to a central SIEM or data lake for correlation.
- Alert on management interface exposure to untrusted networks, including WAN-side access to TCP/80 or TCP/443 on the router.
- Track firmware version inventory across deployed Tenda devices to identify hosts still running 16.03.08.16.
How to Mitigate CVE-2025-10838
Immediate Actions Required
- Restrict the router web management interface to trusted internal hosts only and disable WAN-side administration.
- Change default administrative credentials on all Tenda AC21 devices to reduce the chance of attackers obtaining the low-privilege access needed for exploitation.
- Segment Tenda AC21 routers away from sensitive networks until a vendor fix is applied.
Patch Information
No vendor patch has been published for CVE-2025-10838 at the time of NVD publication on 2025-09-23. Monitor the Tenda Official Site and the VulDB entry #325200 for firmware updates addressing the sub_45BB10 overflow in /goform/WifiExtraSet.
Workarounds
- Disable remote web management on the AC21 and require local LAN access for configuration changes.
- Place the router behind an upstream firewall or ACL that blocks unsolicited inbound connections to its management ports.
- Consider replacing end-of-support Tenda AC21 hardware if the vendor does not release a patch addressing this buffer overflow.
# Example: block external access to the Tenda AC21 web UI from an upstream firewall
# Replace <router_ip> with the AC21 LAN address
iptables -I FORWARD -p tcp -d <router_ip> --dport 80 -j DROP
iptables -I FORWARD -p tcp -d <router_ip> --dport 443 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
