CVE-2026-10233: Out-of-Bounds Read in Assimp Half-Life MDL Loader

Technical summary

CVE-2026-10233 is an out-of-bounds read flaw within the HL1MDLLoader::read_sequence_infos function in HL1MDLLoader.cpp. The vulnerability stems from improper bounds checking when processing the aiString argument during Half-Life 1 MDL file parsing. This permits reading of adjacent memory regions, potentially exposing sensitive data from the process heap or stack. The affected versions extend through Assimp 6.0.4. The flaw combines CWE-119 (improper restriction of operations within the bounds of a memory buffer) and CWE-125 (out-of-bounds read), both classic memory safety issues in C++ codebases handling untrusted file formats.

Business impact

Organizations using Assimp in applications that process user-supplied or untrusted MDL files face a localized information disclosure risk. The threat is primarily relevant to 3D content creation pipelines, game development environments, CAD tools, and multimedia applications. The low CVSS score reflects that exploitation requires local system access and results only in data leakage; integrity and availability are unaffected. For most enterprises, this represents a manageable risk unless Assimp is embedded in customer-facing or internet-exposed tools handling untrusted model files.

Affected systems

Assimp versions up to and including 6.0.4 are vulnerable. The affected component is specifically the Half-Life 1 MDL (model) file loader. Systems most at risk include development workstations, content creation tools, 3D asset pipelines, and any application that parses MDL files from potentially untrusted sources. The vulnerability is not remotely exploitable; an attacker must have local file system access or the ability to place a malicious MDL file where the vulnerable application will load it.

Exploitability

Public disclosure has occurred, and the vulnerability is theoretically exploitable by a local user with file system or user-level access. However, practical exploitation requires that an affected application actually attempt to load a specifically crafted MDL file. The attack vector is local with low privileges required, meaning a standard user account suffices. The low complexity and absence of user interaction requirements (UI:N) make this a straightforward privilege-escalation or lateral-movement vector in multi-user systems where trusted applications parse untrusted model files. The limited scope (information disclosure only) reduces real-world impact.

Remediation

Upgrade Assimp to a patched version released after June 2026 that addresses the bounds checking in HL1MDLLoader::read_sequence_infos. Consult the official Assimp repository and release notes to identify the minimum patched version for your Assimp 6.x line. Until patching is feasible, restrict loading of MDL files to trusted sources, disable MDL loader support if not required, and enforce strict file-type validation before passing files to Assimp. For embedded deployments, consider sandboxing the file-parsing process.

Patch guidance

Monitor the official Assimp GitHub repository (https://github.com/assimp/assimp) for security advisories and version releases that resolve CVE-2026-10233. The vulnerability affects the HL1MDL loader specifically, so ensure that updates to your Assimp dependency include fixes to HL1MDLLoader.cpp. Verify the patched version against the vendor's security advisory before deployment. If you maintain a private fork of Assimp, apply the upstream fix from the official repository to your HL1MDLLoader.cpp file and re-test MDL parsing workflows.

Detection guidance

Monitor application logs and system calls for attempts to load or parse Half-Life 1 MDL files in environments where such files are unexpected. Use static analysis tools (SAST) to scan dependent code and confirm which version of Assimp is linked. Implement software composition analysis (SCA) in your build pipeline to flag Assimp versions up to 6.0.4. If feasible, log file-open operations for .mdl extensions and correlate with the Assimp library loading. Memory access tools (ASAN, Valgrind) during testing can help detect out-of-bounds reads during development.

Why prioritize this

Despite public disclosure, this vulnerability scores LOW (3.3 CVSS) and should be deprioritized relative to critical and high-severity issues. Prioritization rises only if: (1) your organization uses Assimp in production customer-facing tools; (2) those tools accept untrusted 3D model uploads; or (3) a shared development environment runs Assimp where local privilege escalation or lateral movement is a concern. For most enterprises, standard quarterly patching is appropriate. High-priority only if Assimp is embedded in internet-exposed services.

Risk score, explained

The CVSS 3.1 score of 3.3 (LOW) reflects: local attack vector (AV:L) requiring user-level privileges (PR:L), low complexity, no user interaction, and confidentiality impact only (C:L/I:N/A:N). The vulnerability cannot cause denial of service or data modification, limiting fallout to information disclosure of process memory. The public disclosure does increase likelihood of exploitation, but local-only accessibility and the need for file-system interaction significantly constrain threat breadth. Score appropriately reflects a minor risk in most threat models.

Frequently asked questions