CVE-2026-76003: Critical Stack Buffer Overflow in UTT HiPER 1200GW

Overview

A critical stack-based buffer overflow vulnerability has been identified in the UTT HiPER 1200GW broadband router/gateway, affecting all firmware versions up to 2.5.3-170306. The flaw resides in the strcpy call within the /goform/formGroupConfig handler, where the timestart argument is copied into a fixed-size stack buffer without bounds checking.

The vulnerability has been assigned CVE-2026-76003 with a CVSS score of 9.9 (Critical), and a public exploit has been made available.

Technical Details

Vulnerability Mechanism

The formGroupConfig CGI handler processes group scheduling configuration for the device. When parsing the timestart POST parameter, the handler passes the attacker-supplied string directly to strcpy() — a known-unsafe function — without first validating its length against the destination buffer size.

An attacker can submit a crafted HTTP request with an oversized timestart value, overwriting adjacent stack memory including the saved return address. This enables:

• Control-flow hijack — redirect execution to attacker-controlled shellcode or ROP gadgets
• Arbitrary code execution — run commands at the privilege level of the web server process (typically root on embedded devices)
• Persistent backdoor installation — modify firmware, add admin accounts, or disable security features

Because the attack is network-accessible and requires no prior authentication, any device with its management interface exposed to the internet or an untrusted network is at immediate risk.

Affected Products

Note: Other devices in the UTT HiPER product line may share similar code and could be vulnerable to analogous issues. See also CVE-2026-76004 for a related stack overflow in the UTT HiPER 1250GW.

Exploitation

A proof-of-concept exploit has been publicly disclosed. The attack can be performed remotely over the network, making mass exploitation trivial for threat actors scanning for exposed management interfaces.

Risk factors:

• No authentication required
• Exploits a common, well-understood vulnerability class
• PoC publicly available
• Embedded devices often lack runtime mitigations (NX, ASLR, stack canaries)

Recommended Actions

1. Apply vendor patches immediately — check the UTT official site for updated firmware addressing CVE-2026-76003.
2. Restrict management interface access — place the device's web admin interface behind a firewall; do not expose it to the public internet.
3. Network segmentation — isolate affected routers from critical internal systems until patched.
4. Monitor for exploitation — watch for unexpected HTTP POST requests to /goform/formGroupConfig with unusually long timestart values.
5. Replace if unpatched — if no firmware update is available, consider replacing the device with a supported alternative.

References

• NVD — CVE-2026-76003