CVE-2026-15544 Overview
CVE-2026-15544 is a stack-based buffer overflow vulnerability in Shibby Tomato firmware versions up to 1.28.0000. The flaw resides in the getupsvar function within www/apcupsd/tomatodata.cgi, part of the apcupsd component. Attackers can trigger the overflow by manipulating the Field argument through a network-accessible request. The exploit has been publicly disclosed, increasing the risk of active exploitation attempts. The Shibby Tomato project is no longer maintained and has been superseded by FreshTomato.
Critical Impact
Remote attackers with low privileges can exploit the stack-based buffer overflow to corrupt memory, potentially achieving arbitrary code execution on affected router firmware.
Affected Products
- Shibby Tomato firmware versions up to and including 1.28.0000
- apcupsd component (www/apcupsd/tomatodata.cgi)
- Note: This project is superseded by FreshTomato
Discovery Timeline
- 2026-07-13 - CVE CVE-2026-15544 published to NVD
- 2026-07-13 - Last updated in NVD database
Technical Details for CVE-2026-15544
Vulnerability Analysis
The vulnerability exists in the getupsvar function of the tomatodata.cgi CGI script within the apcupsd component. This CGI endpoint exposes UPS status data through the Tomato web interface. The function processes a user-supplied Field parameter without enforcing safe boundary checks before copying it into a fixed-size stack buffer.
The issue is classified as [CWE-119], improper restriction of operations within the bounds of a memory buffer. Because the CGI script executes with elevated privileges on the router, successful exploitation can compromise the integrity, confidentiality, and availability of the device. The EPSS probability for this vulnerability is 0.438%.
Root Cause
The root cause is missing input length validation on the Field argument passed to getupsvar. The function copies attacker-controlled data into a stack-allocated buffer using unbounded string operations. When the input exceeds the buffer size, adjacent stack memory — including saved return addresses — is overwritten. Refer to the Gitee Issue CVE Analysis for the technical breakdown.
Attack Vector
The attack is network-based and requires low privileges on the target device. An authenticated user can send a crafted HTTP request to tomatodata.cgi with an oversized Field parameter targeting the getupsvar handler. Because a public proof-of-concept has been disclosed via VulDB Vulnerability Details, the barrier to weaponization is low. Successful exploitation may result in remote code execution within the router's web service context.
Detection Methods for CVE-2026-15544
Indicators of Compromise
- HTTP requests to /apcupsd/tomatodata.cgi containing unusually long Field query parameters
- Unexpected crashes or restarts of the Tomato httpd service tied to apcupsd requests
- Outbound connections from the router to unfamiliar IP addresses following CGI requests
Detection Strategies
- Inspect web server and CGI logs for requests to tomatodata.cgi with Field values exceeding typical parameter lengths
- Deploy network intrusion detection signatures that match oversized parameters targeting the apcupsd CGI endpoint
- Baseline normal request patterns to the Tomato administrative interface and alert on deviations
Monitoring Recommendations
- Monitor router syslog output for segmentation faults or httpd process termination events
- Track authentication events on the Tomato web interface to identify unauthorized low-privilege access
- Correlate CGI request anomalies with configuration changes or new firewall rules on the device
How to Mitigate CVE-2026-15544
Immediate Actions Required
- Restrict access to the Tomato administrative web interface to trusted management networks only
- Disable the apcupsd feature if UPS integration is not required in the deployment
- Rotate administrative credentials to reduce the risk of low-privilege exploitation by unauthorized users
Patch Information
Shibby Tomato is no longer maintained, and no vendor patch is available for version 1.28.0000 or earlier. The project has been superseded by FreshTomato. Users should migrate to a maintained firmware distribution that receives active security updates. Consult the VulDB CVE Report for reference details.
Workarounds
- Block external access to the router's web management interface at the perimeter
- Remove or rename www/apcupsd/tomatodata.cgi if UPS monitoring is not in use
- Place the router behind a segmentation boundary that filters unauthenticated CGI traffic
- Migrate to FreshTomato or another actively maintained firmware to receive ongoing security fixes
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
