CVE-2025-64183: OpenEXR Use-After-Free Vulnerability

CVE-2025-64183 Overview

CVE-2025-64183 is a use-after-free vulnerability in the OpenEXR image format library, specifically affecting the Python bindings in the legacy adapter code. OpenEXR provides the specification and reference implementation of the EXR file format, which is widely used in the motion picture industry for high dynamic range image storage.

The vulnerability exists in the PyObject_StealAttrString function within pyOpenEXR_old.cpp. This function incorrectly manages Python object references by calling PyObject_GetAttrString to obtain a new reference, immediately decrementing the reference count, and then returning the now-dangling pointer. When callers subsequently pass this pointer to APIs like PyLong_AsLong or PyFloat_AsDouble, a use-after-free condition occurs.

Critical Impact

Applications using the affected OpenEXR Python bindings may experience denial of service through memory corruption when processing EXR files containing specific object attributes such as PixelType.v, Box2i, or V2f.

Affected Products

• OpenEXR versions 3.2.0 through 3.2.4
• OpenEXR versions 3.3.0 through 3.3.5
• OpenEXR versions 3.4.0 through 3.4.2

Discovery Timeline

• 2025-11-10 - CVE-2025-64183 published to NVD
• 2025-12-08 - Last updated in NVD database

Technical Details for CVE-2025-64183

Vulnerability Analysis

This use-after-free vulnerability stems from improper Python object reference counting in the legacy OpenEXR Python adapter. The core issue lies in the PyObject_StealAttrString function which implements incorrect memory management semantics that violate Python's reference counting model.

When the function retrieves an attribute using PyObject_GetAttrString, it receives a new reference to a Python object. However, the function immediately decrements this reference count via Py_DECREF before returning the pointer. This creates a dangling pointer scenario where the memory may be freed or reused by Python's garbage collector while the caller still holds and uses the pointer.

The vulnerability is triggered in multiple code paths throughout the library, including operations that read PixelType.v, Box2i, and V2f attributes from EXR file structures. This widespread invocation pattern increases the attack surface and the likelihood of exploitation during normal file processing operations.

Root Cause

The root cause is a fundamental misunderstanding of Python's reference counting semantics in the legacy adapter code. The PyObject_StealAttrString function attempts to implement "stealing" semantics (transferring ownership without incrementing the reference count), but incorrectly applies this by decrementing the reference count on a newly obtained reference before the caller can safely use the object. The correct implementation should either return a borrowed reference without decrementing, or return a new reference that the caller is responsible for managing.

Attack Vector

This vulnerability requires local access and user interaction to exploit. An attacker could craft a malicious EXR file that, when processed by an application using the vulnerable OpenEXR Python bindings, triggers the use-after-free condition. The attack scenario involves:

1. Creating or modifying an EXR file with specific attribute structures that exercise the vulnerable code paths
2. Having a victim application process the malicious file using the affected Python bindings
3. The resulting memory corruption causes denial of service through application crash

The vulnerability is exploited through the affected Python bindings in pyOpenEXR_old.cpp, specifically at lines 109-115 where PyObject_StealAttrString is defined. When this function is called during attribute access operations (such as reading PixelType.v, Box2i, or V2f values), the returned dangling pointer is passed to conversion functions like PyLong_AsLong or PyFloat_AsDouble, resulting in access to freed memory.

Detection Methods for CVE-2025-64183

Indicators of Compromise

• Application crashes or unexpected termination when processing EXR files using Python bindings
• Memory corruption errors or segmentation faults in Python applications using pyOpenEXR
• Unusual memory access patterns in applications importing OpenEXR Python modules

Detection Strategies

• Monitor for crashes in applications that process EXR files, particularly those using Python-based workflows
• Implement application crash analysis to identify use-after-free patterns in memory dumps
• Use memory sanitizers (AddressSanitizer, Valgrind) during development and testing of applications using OpenEXR Python bindings

Monitoring Recommendations

• Enable crash reporting and analysis for applications in VFX and motion picture production pipelines that handle EXR files
• Monitor system logs for repeated application failures associated with image processing workflows
• Implement file integrity monitoring for incoming EXR files in production environments

How to Mitigate CVE-2025-64183

Immediate Actions Required

• Upgrade OpenEXR to a patched version: 3.2.5, 3.3.6, or 3.4.3 depending on your version branch
• Audit applications that use the OpenEXR Python bindings to identify affected deployments
• Consider temporarily disabling legacy Python adapter functionality if immediate patching is not possible
• Validate EXR files from untrusted sources before processing

Patch Information

Fixed versions have been released by the OpenEXR project. Users should upgrade to one of the following patched versions based on their current deployment:

• Version 3.2.5 for users on the 3.2.x branch
• Version 3.3.6 for users on the 3.3.x branch
• Version 3.4.3 for users on the 3.4.x branch

For detailed patch information and release notes, refer to the OpenEXR Security Advisory GHSA-57cw-j6vp-2p9m.

Workarounds

• Use the newer Python bindings instead of the legacy adapter if your application supports it
• Implement input validation to reject potentially malicious EXR files before processing
• Run applications that process untrusted EXR files in sandboxed environments with limited privileges
• Avoid processing EXR files from untrusted sources until patched versions are deployed