CVE-2026-15548: Shibby Tomato Buffer Overflow Vulnerability

CVE-2026-15548 Overview

CVE-2026-15548 is a stack-based buffer overflow vulnerability affecting Shibby Tomato router firmware up to version 1.28.0000. The flaw resides in the sub_407220 function within /usr/sbin/httpd, specifically in the DNS List Rendering component. An authenticated remote attacker can trigger the overflow over the network to corrupt stack memory. The Shibby Tomato project has been superseded by FreshTomato, meaning affected devices likely no longer receive official security updates. This vulnerability is classified under CWE-119, covering improper restriction of operations within the bounds of a memory buffer.

Critical Impact
Remote exploitation of the stack-based buffer overflow in the httpd daemon can lead to memory corruption, service disruption, and potentially arbitrary code execution on affected Tomato-based routers.

Affected Products

Shibby Tomato firmware versions up to and including 1.28.0000
The /usr/sbin/httpd web management daemon (function sub_407220)
DNS List Rendering component in the Tomato web interface

Discovery Timeline

2026-07-13 - CVE-2026-15548 published to NVD
2026-07-15 - Last updated in NVD database

Technical Details for CVE-2026-15548

Vulnerability Analysis

The vulnerability exists in the sub_407220 function inside the /usr/sbin/httpd binary, which handles rendering of DNS list data in the Tomato router web interface. The function fails to enforce proper bounds when copying attacker-controlled input into a fixed-size stack buffer. Successful exploitation corrupts adjacent stack memory, including saved return addresses and frame pointers.

Because httpd runs on the router with elevated privileges to manage network configuration, memory corruption in this path can compromise the entire device. The attack surface is exposed through the router's web administration interface, which is typically reachable on the LAN and, in misconfigured deployments, from the WAN. According to the CVSS 4.0 vector, exploitation requires low-level authentication but no user interaction.

Root Cause

The root cause is classified under [CWE-119], improper restriction of operations within the bounds of a memory buffer. The sub_407220 routine writes to a stack-allocated buffer without validating the length of the DNS list input against the destination size. This absence of bounds checking permits linear stack corruption when oversized input is supplied through the web management interface.

Attack Vector

An authenticated attacker sends a crafted HTTP request to the Tomato router's management interface containing an oversized DNS list value. When httpd processes the request and invokes sub_407220 to render the DNS entries, the unchecked copy operation overflows the stack buffer. The attack is carried out remotely across the network and does not require user interaction. Technical details are tracked in the VulDB entry for CVE-2026-15548 and the Gitee CVE Issue Discussion.

No verified public exploit code is available at this time. Refer to the linked advisories for further technical analysis rather than synthetic proof-of-concept material.

Detection Methods for CVE-2026-15548

Indicators of Compromise

Unexpected crashes or restarts of the httpd process on Tomato-based routers, particularly following administrative interface access.
HTTP POST requests to router configuration endpoints containing abnormally long DNS list parameters or non-printable byte sequences.
Unauthorized configuration changes or new administrative sessions originating from unusual source addresses.

Detection Strategies

Monitor router system logs and kernel messages for segmentation faults or watchdog-triggered restarts of /usr/sbin/httpd.
Inspect inbound HTTP traffic to router management interfaces for oversized DNS-related form fields that exceed expected input lengths.
Track authentication events on the router web interface, correlating successful logins with subsequent malformed requests to DNS configuration pages.

Monitoring Recommendations

Forward router syslog output to a centralized logging platform and alert on repeated httpd termination or respawn events.
Place Tomato-based routers behind a network segment where management traffic can be inspected by a firewall or IDS.
Establish baselines for normal administrative request sizes so that anomalous, oversized payloads targeting DNS list fields are flagged for review.

How to Mitigate CVE-2026-15548

Immediate Actions Required

Restrict access to the router's web management interface to trusted internal hosts only, and disable remote WAN administration.
Rotate all router administrative credentials and enforce strong, unique passwords to reduce the risk of authenticated exploitation.
Migrate away from Shibby Tomato to an actively maintained firmware such as FreshTomato, which supersedes the vulnerable project.

Patch Information

Shibby Tomato is no longer actively maintained and has been superseded by FreshTomato. No official patch has been published for CVE-2026-15548 in the Shibby Tomato firmware line. Operators should evaluate migration to a maintained fork and monitor upstream FreshTomato releases for any related fixes. Additional context is available at the VulDB CVE-2026-15548 Information page.

Workarounds

Bind the httpd management interface to the LAN only and block TCP access to the management ports from untrusted networks at the perimeter firewall.
Place the router behind a network appliance that terminates and inspects management traffic, dropping requests with oversized DNS-related parameters.
Limit the number of accounts with router administrative privileges, since exploitation requires authenticated access under the CVSS 4.0 vector.

bash

# Example: restrict router management access at the network edge
# Allow only a trusted management host to reach the router web UI
iptables -A INPUT -p tcp -s 192.0.2.10 --dport 80 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP

# Disable remote (WAN) administration via NVRAM on Tomato-based firmware
nvram set remote_management=0
nvram set http_wanport=0
nvram commit
service httpd restart