CVE-2026-16096 Overview
CVE-2026-16096 is a stack-based buffer overflow vulnerability in Shibby Tomato 1.28 RT-N5x MIPSR2 Build 124. The flaw exists in the sub_40BB50 function processing the /proc/webmon_recent_domains file. Attackers can trigger the overflow remotely by manipulating input passed to this function. The Shibby Tomato project has been superseded by FreshTomato, so upstream patches for the original codebase are unlikely. The weakness maps to [CWE-119], improper restriction of operations within the bounds of a memory buffer.
Critical Impact
Remote attackers with low privileges can corrupt stack memory in the Tomato router firmware, potentially leading to code execution or denial of service on affected devices.
Affected Products
- Shibby Tomato firmware version 1.28
- RT-N5x hardware platform (MIPSR2 architecture)
- Build 124
Discovery Timeline
- 2026-07-18 - CVE-2026-16096 published to NVD
- 2026-07-22 - Last updated in NVD database
Technical Details for CVE-2026-16096
Vulnerability Analysis
The vulnerability resides in function sub_40BB50, which handles data associated with the /proc/webmon_recent_domains interface in Shibby Tomato firmware. The function fails to enforce proper bounds when copying attacker-influenced data into a fixed-size stack buffer. When the input length exceeds the destination buffer, adjacent stack memory including saved return addresses is overwritten. On MIPSR2 targets such as the RT-N5x, corruption of the return address on the stack can redirect execution flow to attacker-controlled locations. Because the affected interface is reachable over the network, exploitation does not require local access. The vendor project is no longer maintained, having been replaced by FreshTomato.
Root Cause
The root cause is missing length validation in sub_40BB50 before writing data into a stack-allocated buffer. This category of defect is tracked as [CWE-119], covering unrestricted buffer operations. The web monitoring feature that populates /proc/webmon_recent_domains supplies domain strings that exceed static buffer boundaries.
Attack Vector
Exploitation is network-based and requires low privileges but no user interaction. An authenticated attacker on the router management network can send crafted requests that cause sub_40BB50 to process oversized input. The overflow enables corruption of stack frames on the MIPS target, which can be leveraged for arbitrary code execution or to crash the router process. Technical details are referenced in the Gitee Issue CVE Discussion and the VulDB CVE Report #CVE-2026-16096.
Detection Methods for CVE-2026-16096
Indicators of Compromise
- Unexpected crashes or restarts of the Tomato httpd or web monitoring daemon in system logs
- Anomalously long domain strings appearing in /proc/webmon_recent_domains
- Outbound connections from the router to unknown hosts following administrative requests
- Unauthorized configuration changes to firewall or DNS settings after web session activity
Detection Strategies
- Monitor HTTP requests to Tomato management endpoints for oversized query parameters or headers that could reach sub_40BB50
- Inspect kernel and daemon logs for segmentation faults referencing the web monitor component
- Baseline expected sizes of entries in /proc/webmon_recent_domains and alert on outliers
Monitoring Recommendations
- Forward router syslog output to a centralized log platform for correlation and long-term retention
- Track authentication events on the router administrative interface for brute-force or credential reuse patterns
- Alert on network scans probing router management ports from internal segments
How to Mitigate CVE-2026-16096
Immediate Actions Required
- Restrict access to the router management interface to trusted management VLANs or hosts only
- Disable the web monitoring feature if it is not required for operations
- Rotate administrative credentials on affected devices and enforce strong passwords
- Plan migration off Shibby Tomato to a maintained firmware such as FreshTomato
Patch Information
No official patch is available. The Shibby Tomato project is superseded by FreshTomato, and no vendor advisory has been published for CVE-2026-16096. Operators should evaluate migration to FreshTomato or alternative supported router firmware.
Workarounds
- Block external access to the router web management interface at the perimeter
- Disable webmon (web monitoring) functionality in the Tomato configuration to remove the vulnerable code path
- Segment router management traffic away from untrusted client networks
- Replace end-of-life RT-N5x hardware where firmware migration is not feasible
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
