CVE-2026-40504: Creolabs Gravity RCE Vulnerability

CVE-2026-40504 Overview

CVE-2026-40504 is a critical heap buffer overflow vulnerability in Creolabs Gravity, a lightweight scripting language designed for embedding in applications. The vulnerability exists in the gravity_vm_exec function and allows attackers to write out-of-bounds memory by crafting malicious scripts containing numerous string literals at global scope. Insufficient bounds checking in the gravity_fiber_reassign() function enables heap metadata corruption, potentially leading to arbitrary code execution in applications that evaluate untrusted Gravity scripts.

Critical Impact

Attackers can achieve arbitrary code execution by exploiting heap buffer overflow through crafted Gravity scripts, compromising applications that process untrusted user-supplied scripts.

Affected Products

• Creolabs Gravity versions prior to 0.9.6
• Applications embedding the Gravity scripting language engine
• Development environments utilizing Gravity for script evaluation

Discovery Timeline

• 2026-04-16 - CVE-2026-40504 published to NVD
• 2026-04-16 - Last updated in NVD database

Technical Details for CVE-2026-40504

Vulnerability Analysis

This heap buffer overflow vulnerability (CWE-122) resides in the Gravity virtual machine execution layer. When the Gravity VM processes scripts containing a large number of string literals defined at global scope, the gravity_fiber_reassign() function fails to properly validate buffer boundaries before writing data. This insufficient bounds checking allows memory writes beyond the allocated heap buffer, corrupting adjacent heap metadata structures.

The vulnerability is particularly dangerous because it affects the core script execution engine. Any application that embeds Gravity and allows users to supply scripts—such as game modding frameworks, configuration systems, or automation tools—could be vulnerable to exploitation. The network attack vector indicates that remotely-delivered scripts can trigger this condition without requiring local access.

Root Cause

The root cause stems from inadequate bounds checking within the gravity_fiber_reassign() function when handling fiber (coroutine) reassignment operations during VM execution. When scripts declare numerous string literals at global scope, the function does not properly verify that write operations remain within the allocated buffer boundaries. This oversight allows controlled out-of-bounds writes that can corrupt heap metadata, enabling attackers to manipulate memory allocation behavior and potentially redirect execution flow.

Attack Vector

The attack vector involves crafting a malicious Gravity script that declares an excessive number of string literals at global scope. When this script is parsed and executed by the Gravity VM, the gravity_vm_exec function processes these literals, eventually triggering the vulnerable code path in gravity_fiber_reassign(). The attacker-controlled heap corruption can be leveraged to:

1. Overwrite function pointers or vtable entries
2. Corrupt heap metadata to achieve write-what-where conditions
3. Hijack control flow to execute arbitrary shellcode

Applications processing untrusted scripts from network sources, user uploads, or plugin systems are at elevated risk. The vulnerability requires no authentication or user interaction beyond script submission, making it exploitable in automated pipelines.

The vulnerability mechanism involves insufficient validation in the fiber reassignment function during script execution. When many string literals are declared at global scope, the internal buffer handling fails to enforce proper boundaries. Technical details are available in the GitHub Issue Discussion and the VulnCheck Security Advisory.

Detection Methods for CVE-2026-40504

Indicators of Compromise

• Gravity scripts containing unusually high numbers of string literal declarations at global scope
• Application crashes or unexpected terminations in processes utilizing the Gravity VM
• Memory corruption errors or heap integrity violations in application logs
• Abnormal memory allocation patterns in applications embedding Gravity

Detection Strategies

• Monitor for scripts with excessive global-scope string literals exceeding normal thresholds
• Implement runtime heap integrity checking in applications embedding Gravity
• Deploy application-level input validation to limit script complexity before VM execution
• Use memory sanitizers (ASan, MSan) during development and testing of Gravity-integrated applications

Monitoring Recommendations

• Enable crash dump collection and analysis for applications using Gravity scripting
• Implement logging around script submission and execution endpoints
• Monitor process memory usage for anomalous growth patterns during script evaluation
• Configure alerting for heap corruption detection mechanisms in production environments

How to Mitigate CVE-2026-40504

Immediate Actions Required

• Upgrade Creolabs Gravity to version 0.9.6 or later immediately
• Audit all applications embedding Gravity to identify vulnerable deployments
• Restrict or disable untrusted script execution until patches are applied
• Implement script validation and sandboxing as defense-in-depth measures

Patch Information

Creolabs has released version 0.9.6 which addresses this heap buffer overflow vulnerability. The fix is available through the GitHub Release Version 0.9.6. The specific commit addressing this vulnerability can be reviewed at the GitHub Commit Update.

Organizations should prioritize updating all Gravity installations and rebuilding applications that statically link the Gravity library. For dynamically linked deployments, replacing the shared library with the patched version is sufficient.

Workarounds

• Implement strict input validation to limit the number of string literals permitted in submitted scripts
• Deploy script execution within sandboxed environments with restricted memory access
• Use process isolation techniques to contain potential exploitation impact
• Consider script pre-processing to reject scripts exceeding safe complexity thresholds

# Configuration example - Upgrade Gravity to patched version
git clone https://github.com/marcobambini/gravity.git
cd gravity
git checkout 0.9.6
make clean && make
sudo make install