CVE-2026-2655: ChaiScript Use After Free Vulnerability

CVE-2026-2655 Overview

A use after free vulnerability has been identified in ChaiScript up to version 6.1.0. The vulnerability affects the chaiscript::str_less::operator function located in the file include/chaiscript/chaiscript_defines.hpp. This memory corruption flaw can be exploited locally, though it requires a high level of complexity to successfully leverage.

Critical Impact

While this vulnerability has a low severity rating, the use after free condition could potentially lead to denial of service conditions in applications embedding the ChaiScript scripting engine.

Affected Products

• ChaiScript versions up to 6.1.0
• Applications embedding the ChaiScript scripting engine
• Systems utilizing chaiscript::str_less::operator functionality

Discovery Timeline

• February 18, 2026 - CVE-2026-2655 published to NVD
• February 19, 2026 - Last updated in NVD database

Technical Details for CVE-2026-2655

Vulnerability Analysis

This vulnerability is classified as a Use After Free (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) condition within the ChaiScript embedded scripting language. The flaw exists in the string comparison operator implementation chaiscript::str_less::operator found in the header file include/chaiscript/chaiscript_defines.hpp.

Use after free vulnerabilities occur when a program continues to use memory after it has been freed, potentially allowing an attacker to manipulate program execution or cause unexpected behavior. In this case, the vulnerability requires local access to exploit and presents high attack complexity, making successful exploitation difficult.

The vulnerability has been publicly disclosed, and proof-of-concept information exists in the wild. The ChaiScript project maintainers were notified through GitHub Issue #632 but have not yet responded to the report.

Root Cause

The root cause of this vulnerability lies in improper memory management within the chaiscript::str_less::operator function. The function appears to access memory that has already been deallocated, creating a dangling pointer condition. This type of error typically occurs when:

• Memory is freed but pointers to that memory are not properly invalidated
• Object lifetimes are not correctly managed during string comparison operations
• Reference counting or smart pointer mechanisms fail to prevent premature deallocation

Attack Vector

The attack vector for CVE-2026-2655 requires local access to the system running an application that embeds ChaiScript. An attacker would need to craft specific input that triggers the vulnerable code path in the string comparison operator.

Due to the high complexity requirement, successful exploitation necessitates:

• Understanding of the ChaiScript memory layout
• Ability to control timing and memory allocation patterns
• Local execution context with appropriate privileges to interact with the target application

The vulnerability primarily affects availability, potentially causing application crashes or denial of service conditions rather than enabling code execution or information disclosure.

Detection Methods for CVE-2026-2655

Indicators of Compromise

• Application crashes or unexpected terminations in ChaiScript-embedded applications
• Memory access violations or segmentation faults during script execution
• Abnormal memory consumption patterns indicating potential use after free exploitation attempts

Detection Strategies

• Deploy memory debugging tools such as AddressSanitizer (ASan) to detect use after free conditions at runtime
• Monitor application logs for crashes originating from ChaiScript components
• Implement static analysis scanning for vulnerable ChaiScript versions in software dependencies
• Review application crash dumps for stack traces involving chaiscript::str_less::operator

Monitoring Recommendations

• Enable core dump collection for ChaiScript-embedded applications to analyze crash events
• Implement dependency scanning in CI/CD pipelines to identify vulnerable ChaiScript versions
• Monitor system stability metrics for applications utilizing ChaiScript scripting functionality

How to Mitigate CVE-2026-2655

Immediate Actions Required

• Audit applications for ChaiScript dependencies and identify versions up to 6.1.0
• Consider isolating ChaiScript scripting functionality with sandboxing techniques
• Restrict local access to systems running vulnerable ChaiScript-embedded applications
• Monitor the official ChaiScript repository for security updates

Patch Information

At the time of this writing, no official patch has been released by the ChaiScript maintainers. The project was notified of the vulnerability through GitHub Issue #632 but has not yet responded. Organizations should monitor the ChaiScript GitHub repository for future security releases and apply patches as soon as they become available.

Workarounds

• Limit untrusted input to ChaiScript interpreters to reduce the attack surface
• Implement application-level sandboxing around ChaiScript execution contexts
• Consider compiling ChaiScript with AddressSanitizer during development to catch memory errors early
• Evaluate alternative scripting engines if ChaiScript functionality is not critical to operations

# Build ChaiScript with AddressSanitizer for development/testing
cmake -DCMAKE_CXX_FLAGS="-fsanitize=address -g" ..
make

# Run tests with ASan to detect memory issues
ASAN_OPTIONS=detect_stack_use_after_return=1 ./chaiscript_test