CVE-2026-2656: ChaiScript Use-After-Free Vulnerability

CVE-2026-2656 Overview

A use after free vulnerability has been discovered in ChaiScript versions up to 6.1.0. This flaw specifically affects the function chaiscript::Type_Info::bare_equal located in the file include/chaiscript/dispatchkit/type_info.hpp. The vulnerability requires local access to exploit and has been assessed as having high complexity with difficult exploitability. The exploit has been published and may be used. The ChaiScript project was notified of this issue through a GitHub issue report but has not yet responded.

Critical Impact

Local attackers with low privileges can potentially cause limited availability impact through memory corruption by triggering a use after free condition in ChaiScript's type information handling mechanism.

Affected Products

• ChaiScript versions up to and including 6.1.0
• Applications embedding ChaiScript scripting engine
• Systems processing untrusted ChaiScript scripts

Discovery Timeline

• 2026-02-18 - CVE-2026-2656 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2026-2656

Vulnerability Analysis

This vulnerability is classified as a use after free (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw exists in the chaiscript::Type_Info::bare_equal function within the ChaiScript type dispatching system. Use after free vulnerabilities occur when a program continues to use a pointer after the memory it references has been freed, potentially leading to memory corruption, crashes, or in some cases, code execution.

The attack requires local access to the system and the ability to execute ChaiScript code. While the complexity is rated as high and exploitability is difficult, the vulnerability has been publicly disclosed with exploit details available.

Root Cause

The root cause lies in improper memory management within ChaiScript's type information comparison functionality. The bare_equal function in type_info.hpp appears to access memory that has been previously deallocated, creating a dangling pointer situation. This typically occurs when type information objects are compared after one of them has gone out of scope or been explicitly freed, but references to it remain in use.

Attack Vector

The attack vector is local, requiring an attacker to have the ability to execute code on the target system. An attacker would need to craft malicious ChaiScript code that manipulates type information objects in a specific sequence to trigger the use after free condition. The manipulation involves creating and destroying type objects in a manner that causes the bare_equal function to operate on freed memory.

The vulnerability manifests when comparing type information objects in ChaiScript's dispatch system. Attackers can potentially trigger this condition by crafting scripts that manipulate object lifecycles in specific patterns. Technical details and proof of concept information are available in GitHub Issue #636.

Detection Methods for CVE-2026-2656

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications using ChaiScript
• Abnormal memory access patterns in processes executing ChaiScript scripts
• Application crashes specifically within type_info.hpp related stack traces
• Memory corruption errors logged by address sanitizers or similar tools

Detection Strategies

• Monitor for application crashes involving ChaiScript components or bare_equal function calls
• Implement memory sanitizers (AddressSanitizer, Valgrind) in development and testing environments to detect use after free conditions
• Review application logs for segmentation faults or memory access violations in ChaiScript execution paths
• Deploy runtime application self-protection (RASP) solutions to detect memory corruption attempts

Monitoring Recommendations

• Enable detailed crash reporting for applications embedding ChaiScript
• Configure system monitoring to alert on repeated application crashes
• Audit the sources of ChaiScript scripts being executed to ensure they are from trusted origins
• Implement application-level logging around ChaiScript script execution

How to Mitigate CVE-2026-2656

Immediate Actions Required

• Assess applications in your environment that embed ChaiScript versions up to 6.1.0
• Restrict execution of untrusted ChaiScript scripts until a patch is available
• Consider sandboxing ChaiScript execution environments with reduced privileges
• Monitor the ChaiScript GitHub repository for vendor response and patches

Patch Information

As of the last update, the ChaiScript project has been notified through GitHub Issue #636 but has not yet responded with a patch. Users should monitor the official ChaiScript repository for security updates and apply patches as soon as they become available.

Workarounds

• Only execute ChaiScript code from trusted and verified sources
• Implement input validation for any external ChaiScript script inputs
• Consider compiling applications with memory safety hardening flags and address space layout randomization (ASLR)
• Deploy applications using ChaiScript in sandboxed or containerized environments with limited system access

# Configuration example - Build ChaiScript applications with memory safety options
# When compiling applications that use ChaiScript, enable memory safety features:
g++ -fsanitize=address -fno-omit-frame-pointer -g your_app.cpp -o your_app
# Run applications in restricted environments
# Consider using containers with limited permissions
docker run --read-only --security-opt=no-new-privileges your-chaiscript-app