CVE-2026-76004: Critical Stack Buffer Overflow in UTT HiPER 1250GW HTTP Handler

Overview

A critical stack-based buffer overflow has been discovered in the UTT HiPER 1250GW broadband gateway, affecting firmware versions up to 3.2.7-210907-180535. The vulnerability exists in the strcpy call within the /goform/aspApBasicConfigUrcp endpoint's HTTP handler, where the pvid parameter is written to a fixed-size stack buffer with no bounds validation.

Tracked as CVE-2026-76004 with a CVSS score of 9.9 (Critical), the flaw is remotely exploitable with no authentication required, and a public exploit has been released.

Technical Details

Vulnerability Mechanism

The /goform/aspApBasicConfigUrcp handler processes basic AP/URCP configuration submissions for the HiPER 1250GW. When handling the pvid (VLAN ID) parameter from an HTTP request, the code passes the raw user-supplied value directly into strcpy(), writing it to a stack-allocated buffer without verifying that the input fits within the buffer's declared size.

An attacker sending a crafted HTTP request with an oversized pvid value can:

1. Overflow the stack buffer — overwrite the function's return address and adjacent stack data
2. Hijack control flow — redirect execution to an attacker-supplied payload or ROP chain
3. Execute arbitrary code — run commands with the privileges of the web server process (typically root on consumer/SOHO gateways)

Embedded devices often lack modern exploit mitigations (stack canaries, ASLR, non-executable stacks), making this class of vulnerability particularly reliable to exploit.

Affected Products

Note: This vulnerability is closely related to CVE-2026-76003, a similar strcpy stack overflow in the UTT HiPER 1200GW. Both vulnerabilities were disclosed concurrently, suggesting a broader pattern of unsafe string handling across the UTT HiPER product line.

Exploitation

A proof-of-concept exploit has been publicly disclosed alongside the CVE publication. The combination of network accessibility, no authentication requirement, and public PoC code significantly raises the risk of active exploitation in the wild.

Compounding factors:

• SOHO/SMB routers are frequently unmanaged and rarely patched
• Management interfaces are sometimes unintentionally exposed to the internet via port forwarding or misconfiguration
• Embedded Linux firmware typically lacks stack canaries, making exploitation straightforward
• The PoC lowers the barrier for less sophisticated threat actors

Recommended Actions

1. Patch immediately — check the UTT website for firmware updates that address CVE-2026-76004.
2. Restrict management access — block all inbound access to the device's web admin interface from untrusted networks; use ACLs or a dedicated management VLAN.
3. Audit internet exposure — verify that no port forwarding rules expose port 80/443 of the router admin interface to the internet.
4. Detection — monitor HTTP logs for POST requests to /goform/aspApBasicConfigUrcp with unusually long pvid values.
5. Consider replacement — if a patch is not forthcoming, replace affected hardware with a supported, actively maintained device.

References

• NVD — CVE-2026-76004
• CVE-2026-76003 — Related UTT HiPER 1200GW Flaw