CVE-2026-2659: Squirrel Buffer Overflow Vulnerability

CVE-2026-2659 Overview

A vulnerability has been identified in Squirrel, a lightweight scripting language, affecting versions up to 3.2. The vulnerability exists in the function SQFuncState::PopTarget within the file src/squirrel/squirrel/sqfuncstate.cpp. By manipulating the _target_stack argument, an attacker can trigger an out-of-bounds read condition. This vulnerability requires local access to exploit and has been publicly disclosed with a reproduction case available.

Critical Impact

Local attackers can trigger out-of-bounds memory reads by manipulating the _target_stack argument, potentially leading to information disclosure or application crashes. The exploit has been publicly disclosed while the vendor has not yet responded to the security report.

Affected Products

• Squirrel up to version 3.2
• Applications embedding the Squirrel scripting language
• Game engines and embedded systems using Squirrel as a scripting interface

Discovery Timeline

• 2026-02-18 - CVE-2026-2659 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2026-2659

Vulnerability Analysis

This out-of-bounds read vulnerability (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) occurs in the Squirrel scripting language's function state management code. The SQFuncState::PopTarget function fails to properly validate boundaries when accessing elements from the _target_stack data structure. When specially crafted input manipulates this stack, the function attempts to read memory outside the allocated buffer boundaries.

The vulnerability is classified as a local attack vector, meaning an attacker would need to provide malicious Squirrel scripts or manipulate script execution on the target system. While the direct impact is limited to availability (potential crashes), out-of-bounds read vulnerabilities can sometimes be chained with other exploits to achieve information disclosure or be leveraged as part of more sophisticated attack chains.

The project maintainers were notified early through an issue report but have not responded at the time of disclosure.

Root Cause

The root cause lies in insufficient bounds checking within the SQFuncState::PopTarget function in sqfuncstate.cpp. When the function processes the _target_stack argument, it does not adequately verify that the index or pointer remains within the valid memory region allocated for the stack. This allows specially crafted inputs to force the function to access memory locations outside the intended boundaries.

Attack Vector

The attack requires local access to the system where Squirrel scripts are executed. An attacker would craft a malicious Squirrel script or manipulate the function state in a way that causes _target_stack to reference an invalid memory location. When SQFuncState::PopTarget is subsequently called, it reads from the manipulated address, triggering the out-of-bounds read condition.

The vulnerability manifests during script compilation or execution when the function state stack is manipulated beyond its intended bounds. A reproduction case demonstrating this vulnerability is available through the GitHub Reproduction Case linked in the external references.

Detection Methods for CVE-2026-2659

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications using Squirrel scripting
• Memory access violations reported in application logs during script execution
• Abnormal behavior when processing untrusted Squirrel scripts
• Core dumps indicating memory corruption in sqfuncstate.cpp or related components

Detection Strategies

• Implement memory sanitizers (ASan, MSan) during development and testing to detect out-of-bounds access
• Monitor application crash dumps for stack traces referencing SQFuncState::PopTarget or sqfuncstate.cpp
• Deploy runtime application self-protection (RASP) solutions to detect memory violation attempts
• Review logs for repeated script execution failures that may indicate exploitation attempts

Monitoring Recommendations

• Enable verbose logging for Squirrel script execution to capture error conditions
• Configure crash reporting to alert security teams when memory-related exceptions occur
• Implement canary-based monitoring for applications that process untrusted scripts
• Monitor system stability metrics for applications embedding Squirrel

How to Mitigate CVE-2026-2659

Immediate Actions Required

• Restrict execution of untrusted Squirrel scripts until a patch is available
• Implement input validation and sandboxing for Squirrel script execution
• Consider disabling Squirrel scripting functionality in production if not critical
• Review and audit any externally-sourced Squirrel scripts before execution

Patch Information

At the time of this writing, the Squirrel project maintainers have not responded to the security report submitted via the GitHub Issue Report. No official patch is currently available. Organizations using Squirrel should monitor the project repository for updates and apply patches as soon as they become available.

Additional vulnerability details can be found at VulDB #346457 Details.

Workarounds

• Sandbox Squirrel script execution using operating system-level isolation (containers, VMs, or restricted user accounts)
• Implement application-level bounds checking before calling SQFuncState::PopTarget
• Use memory-safe compilation options (stack protectors, ASLR) to reduce exploitation potential
• Consider temporarily switching to alternative scripting solutions if untrusted scripts must be processed

# Example: Compile with memory safety features enabled
# Add these flags when building applications that use Squirrel
CXXFLAGS="-fstack-protector-strong -D_FORTIFY_SOURCE=2 -fsanitize=address"

# Run with AddressSanitizer to detect memory issues during testing
ASAN_OPTIONS=detect_oob_access=1:halt_on_error=0 ./your_application