CVE-2026-82591: Assimp Library Buffer Overflow Vulnerability

CVE-2026-82591 Overview

CVE-2026-82591 is a heap-based buffer overflow vulnerability in the Open Asset Import Library (Assimp) affecting versions up to 6.0.2. The flaw resides in the MD5Importer::MakeDataUnique function within code/AssetLib/MD5/MD5Loader.cpp. Manipulation of the iNewIndex argument triggers an out-of-bounds write on the heap. The vulnerability is categorized as [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). Exploitation requires local access and low privileges, limiting remote attack scenarios. The maintainers have published a patch referenced by commit hash bf9dabb617c46e5133dac65cca6bff177917afcb.

Critical Impact
A local attacker supplying a crafted MD5 model file can trigger a heap-based buffer overflow in applications that load 3D assets through Assimp, potentially corrupting memory and impacting confidentiality, integrity, and availability of the host process.

Affected Products

Open Asset Import Library (Assimp) versions up to and including 6.0.2
Applications and game engines that embed the vulnerable MD5Loader component
Downstream 3D content pipelines relying on Assimp for MD5 model import

Discovery Timeline

2026-08-30 - CVE-2026-82591 published to NVD
2026-09-01 - Last updated in NVD database

Technical Details for CVE-2026-82591

Vulnerability Analysis

The defect lives in Assimp's MD5 model loader, a parser for id Software's MD5 mesh and animation format. During deduplication of vertex data, the MD5Importer::MakeDataUnique function computes a new index value stored in iNewIndex. That index is used to reference heap-allocated buffers holding vertex, weight, or face data. Because the loader does not properly enforce boundary conditions on the derived index, a malformed MD5 asset can drive writes past the end of the allocated region. The result is heap memory corruption within the process embedding Assimp. Assimp is used in game engines, 3D asset pipelines, and modeling tools, which broadens the exposure surface for applications that automatically import untrusted models.

Root Cause

The root cause is missing bounds validation on the iNewIndex argument inside MD5Importer::MakeDataUnique. The function trusts values derived from parsed file content without ensuring they fall within the size of the destination buffer. This maps to [CWE-119], where an operation reads or writes outside the intended memory boundaries. Attacker-controlled fields in the MD5 file drive the calculation, allowing precise placement of the out-of-bounds write.

Attack Vector

Exploitation requires the victim to open or process a malicious MD5 model file with an application that links against a vulnerable Assimp build. The attack vector is local: an attacker must deliver the crafted file to the target system and cause it to be parsed. Successful exploitation corrupts heap metadata or adjacent objects, which can lead to process crashes or, depending on heap layout and mitigations, controlled memory manipulation. No network-based exploitation path has been reported. Public proof-of-concept exploit code was not available at the time of publication. See the GitHub Commit Update and GitHub Pull Request #6718 for technical details of the fix.

Detection Methods for CVE-2026-82591

Indicators of Compromise

Crashes, aborts, or heap corruption messages originating from processes that load MD5 model files through Assimp.
Presence of untrusted .md5mesh or .md5anim files in asset directories consumed by 3D applications.
Unexpected child process spawning or shellcode-like memory regions in tools that import 3D assets.

Detection Strategies

Inventory binaries and applications that ship or dynamically link libassimp and identify versions at or below 6.0.2.
Use software composition analysis (SCA) to flag builds referencing vulnerable Assimp commits prior to bf9dabb617c46e5133dac65cca6bff177917afcb.
Enable address sanitizer (ASan) or equivalent heap protections in development and QA pipelines that process MD5 assets.

Monitoring Recommendations

Alert on application crash telemetry (Windows Error Reporting, macOS ReportCrash, Linux abrt) for processes that parse 3D assets.
Log and review file drops of MD5-format assets from untrusted sources such as email, browser downloads, or removable media.
Track behavioral anomalies in modeling and gaming applications immediately after loading external content.

How to Mitigate CVE-2026-82591

Immediate Actions Required

Update Assimp to a version that includes commit bf9dabb617c46e5133dac65cca6bff177917afcb and rebuild downstream applications against the fixed library.
Restrict processing of MD5 model files to trusted sources until the patched version is deployed.
Audit application inventories for statically linked or vendored copies of Assimp that require independent patching.

Patch Information

The upstream fix is available in the Assimp project via commit bf9dabb617c46e5133dac65cca6bff177917afcb, merged through GitHub Pull Request #6718. Applying the patch is the vendor-recommended action. Additional references are available at VulDB CVE-2026-82591 and VulDB Vulnerability #397086.

Workarounds

Disable the MD5 importer at build time or via runtime configuration for applications that do not require MD5 asset support.
Sandbox asset-importing processes using OS-level containment such as AppContainer, seccomp, or macOS App Sandbox to reduce blast radius.
Enforce file-type allowlists and content validation before passing user-supplied models to Assimp.

bash

# Rebuild Assimp from source with the security patch applied
git clone https://github.com/assimp/assimp.git
cd assimp
git checkout bf9dabb617c46e5133dac65cca6bff177917afcb
cmake -S . -B build -DASSIMP_BUILD_MD5_IMPORTER=OFF
cmake --build build --config Release