CVE-2026-2258: Lobster Buffer Overflow Vulnerability

CVE-2026-2258 Overview

A memory corruption vulnerability has been identified in the aardappel lobster programming language up to version 2025.4. The vulnerability exists in the WaveFunctionCollapse function within the dev/src/lobster/wfc.h library file. By executing a manipulation with crafted input, an attacker can trigger memory corruption. This is a local attack vector requiring the attacker to have local access to execute malicious code.

Critical Impact

Local attackers can cause memory corruption by providing illegal character inputs to the WaveFunctionCollapse function, potentially leading to application instability or denial of service.

Affected Products

• aardappel lobster up to version 2025.4
• Applications using the lobster WFC (Wave Function Collapse) library
• Systems running unpatched lobster installations

Discovery Timeline

• 2026-02-10 - CVE CVE-2026-2258 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-2258

Vulnerability Analysis

The vulnerability resides in the Wave Function Collapse algorithm implementation within the lobster programming language. The WaveFunctionCollapse function in dev/src/lobster/wfc.h expects input tile characters to be within the range 0..127, with a maximum of 64 unique tiles actually in use. However, the original implementation failed to properly validate that input characters fell within this expected range.

When characters outside the 0..127 range are provided as input, the function does not detect these as invalid, leading to memory corruption. The local attack vector means an attacker would need to craft a malicious lobster script or input file that triggers the WaveFunctionCollapse function with out-of-range character values.

Root Cause

The root cause is an improper input validation error (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The WaveFunctionCollapse function did not check whether input characters were within the valid 0..127 range before processing them. This missing boundary check allows out-of-range values to cause buffer operations beyond expected memory boundaries.

Attack Vector

The attack requires local access to execute a crafted lobster script or provide malicious input to an application using the lobster WFC library. An attacker would:

1. Create input data containing characters outside the valid 0..127 range
2. Execute a lobster program that calls the wave_function_collapse function with this crafted input
3. Trigger memory corruption when the function processes the illegal characters

The following patch demonstrates the security fix applied to address this vulnerability:

// inmap & outmap must point to row-major 2D arrays of the given size.
// each in tile char must be in range 0..127, of which max 64 may actually be in use (may be
// sparse).
-// Returns false if too many unique tiles in input.
+// Returns false if too many unique tiles in input, or a char out of range 0..127.
template<typename T> bool WaveFunctionCollapse(const int2 &insize, const char **inmap,
                                               const int2 &outsize, char **outmap,
                                               RandomNumberGenerator<T> &rnd,

Source: GitHub Commit Details

The corresponding error handling in builtins.cpp was also updated:

        auto ok = WaveFunctionCollapse(int2(iint2(cols, ssize(inmap))), inmap.data(), sz, outmap.data(),
                                       vm.rndx[vm.active_rng], num_contradictions);
        if (!ok)
-            vm.BuiltinError("tilemap contained too many tile ids");
+            vm.BuiltinError("tilemap contained too many tile ids, or characters outside of 0..127 range");
        Push(sp,  outstrings);
        Push(sp,  num_contradictions);
    });

Source: GitHub Commit Details

Detection Methods for CVE-2026-2258

Indicators of Compromise

• Unexpected application crashes when processing Wave Function Collapse operations
• Error messages related to tilemap processing or tile ID issues in lobster applications
• Malformed lobster script files containing characters outside standard ASCII range
• Unusual memory consumption patterns in lobster runtime processes

Detection Strategies

• Monitor lobster application logs for errors related to WaveFunctionCollapse function failures
• Implement file integrity monitoring on lobster script files to detect potential malicious modifications
• Deploy runtime application self-protection (RASP) to detect memory corruption attempts
• Use SentinelOne's behavioral AI to identify anomalous memory access patterns in lobster processes

Monitoring Recommendations

• Enable verbose logging in lobster applications to capture WFC function calls and their parameters
• Monitor process memory usage for unexpected spikes during tile map generation operations
• Implement input validation at application boundaries before data reaches the lobster WFC library
• Configure alerting for repeated application crashes in lobster-based systems

How to Mitigate CVE-2026-2258

Immediate Actions Required

• Apply the security patch identified by commit c2047a33e1ac2c42ab7e8704b33f7ea518a11ffd immediately
• Review any custom scripts or input files used with the WaveFunctionCollapse function
• Restrict local access to systems running lobster applications to trusted users only
• Validate all inputs to lobster WFC functions at the application layer as an additional defense

Patch Information

The vulnerability has been addressed in commit c2047a33e1ac2c42ab7e8704b33f7ea518a11ffd in the aardappel lobster repository. The patch adds validation to ensure input characters are within the valid 0..127 range before processing. Organizations should update to a version of lobster that includes this commit. Additional details about the fix can be found in the GitHub Issue Tracker.

Workarounds

• Implement application-level input validation to filter characters outside the 0..127 range before passing data to WaveFunctionCollapse
• Restrict execution of lobster scripts to trusted, reviewed code only
• Run lobster applications in sandboxed environments with limited memory access permissions
• Consider disabling WFC functionality if not required until the patch can be applied

# Clone and update to patched version
git clone https://github.com/aardappel/lobster.git
cd lobster
git checkout c2047a33e1ac2c42ab7e8704b33f7ea518a11ffd
# Rebuild the lobster interpreter with the fix
make clean && make