CVE-2025-2756: Assimp Buffer Overflow Vulnerability

CVE-2025-2756 Overview

CVE-2025-2756 is a heap-based buffer overflow vulnerability in Open Asset Import Library (Assimp) version 5.4.3. The flaw resides in the Assimp::AC3DImporter::ConvertObjectSection function within code/AssetLib/AC/ACLoader.cpp, part of the AC3D file handler component. Improper handling of the tmp argument allows an attacker to corrupt heap memory when a crafted AC3D model file is parsed. The vulnerability is categorized under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). Public disclosure of the exploit details has occurred, increasing the risk that opportunistic attackers will weaponize the flaw against applications that embed Assimp for 3D asset processing.

Critical Impact

Remote attackers can trigger heap corruption in any application using Assimp 5.4.3 by supplying a malicious AC3D file, enabling potential memory disclosure, denial of service, or code execution.

Affected Products

• Open Asset Import Library (Assimp) 5.4.3
• Applications and game engines statically or dynamically linked against the affected assimp library
• Pipelines and tools that automatically import AC3D (.ac) assets via Assimp

Discovery Timeline

• 2025-03-25 - CVE-2025-2756 published to NVD
• 2025-07-17 - Last updated in NVD database

Technical Details for CVE-2025-2756

Vulnerability Analysis

Assimp is a widely deployed open-source library that parses dozens of 3D model formats, including the legacy AC3D format used by tools such as AC3D and FlightGear. The ConvertObjectSection routine in ACLoader.cpp processes object sections inside an AC3D file and writes parsed data into a heap-allocated buffer referenced by the tmp argument. The loader does not adequately validate the relationship between counts declared in the file and the size of the destination buffer. A crafted AC3D file can cause writes past the allocated boundary, producing a heap-based buffer overflow.

The consequence depends on the host application. Confidentiality, integrity, and availability impacts are each rated low, consistent with a memory corruption issue that may lead to crashes, information disclosure through adjacent heap data, or, under favorable allocator conditions, code execution.

Root Cause

The root cause is missing bounds enforcement on attacker-controlled size fields parsed from the AC3D input. The tmp buffer is sized based on assumptions that do not hold for adversarial inputs, and subsequent writes use file-derived counters without validation against the actual allocation length.

Attack Vector

Exploitation requires a victim to open or import a malicious AC3D file. The attack is network-reachable through any application that ingests user-supplied 3D assets, including modeling tools, game launchers, asset converters, and web services that perform server-side mesh processing. User interaction is typically required to load the file. The vulnerability manifests in the AC3D parser; refer to the GitHub Issue Discussion for technical details and reproducer information.

Detection Methods for CVE-2025-2756

Indicators of Compromise

• Unexpected crashes, segmentation faults, or heap corruption errors in processes loading .ac files through Assimp
• AC3D files originating from untrusted sources that contain anomalously large object section counters
• Allocator diagnostic messages such as glibc malloc(): corrupted or AddressSanitizer heap-buffer-overflow reports tied to ACLoader.cpp

Detection Strategies

• Run Assimp-linked binaries under AddressSanitizer or HardenedMalloc in test environments to surface out-of-bounds writes in ConvertObjectSection
• Inspect ingestion pipelines for AC3D imports and log file hashes for offline triage of suspicious assets
• Use software composition analysis (SCA) tooling to inventory applications shipping assimp 5.4.3 across the estate

Monitoring Recommendations

• Alert on crash telemetry from desktop and server processes that include assimp modules in their stack traces
• Monitor file upload endpoints for .ac extensions or AC3D magic bytes (AC3D) and quarantine for review
• Track process integrity and child-process behavior of applications that parse 3D content, since post-exploitation activity often spawns shells or downloaders

How to Mitigate CVE-2025-2756

Immediate Actions Required

• Identify every application and service that bundles Assimp 5.4.3 and prioritize those exposed to untrusted file input
• Disable AC3D import paths in affected applications where the format is not business-critical
• Restrict upload and ingestion of .ac files at perimeter and application layers until a fixed build is deployed

Patch Information

At the time of NVD publication, the upstream Assimp project tracked the issue in Assimp GitHub Issue #6018. Administrators should monitor that issue and the Assimp release page for a fixed version that supersedes 5.4.3, then rebuild or update any downstream software that statically links the library. Additional vulnerability metadata is available via VulDB entry 300861.

Workarounds

• Strip or block AC3D files at email gateways, content-disarm-and-reconstruction (CDR) systems, and web upload handlers
• Sandbox asset import processes using OS-level isolation such as seccomp, AppArmor, or Windows AppContainer to limit blast radius of heap corruption
• Process untrusted 3D assets in ephemeral virtual machines or containers with no network egress and minimal filesystem access

# Configuration example: block AC3D uploads at an Nginx ingestion endpoint
location /upload {
    if ($request_filename ~* \.ac$) {
        return 403;
    }
    client_max_body_size 25m;
    proxy_pass http://asset_pipeline;
}