CVE-2026-40244: OpenEXR Buffer Overflow Vulnerability

CVE-2026-40244 Overview

CVE-2026-40244 is a high-severity integer overflow vulnerability affecting OpenEXR, the specification and reference implementation of the EXR file format widely used in the motion picture and visual effects industry. The vulnerability exists in the DWA (DWAA/DWAB) compressor component where an arithmetic operation performs integer multiplication without proper type casting, potentially leading to memory corruption and code execution.

Critical Impact

Attackers can exploit this integer overflow by crafting malicious EXR files that, when processed by vulnerable OpenEXR versions, may cause heap corruption leading to arbitrary code execution or denial of service. This is particularly concerning for media production environments where EXR files are routinely processed from external sources.

Affected Products

• OpenEXR versions 3.4.0 through 3.4.9
• OpenEXR versions 3.3.0 through 3.3.9
• OpenEXR versions 3.2.0 through 3.2.7

Discovery Timeline

• 2026-04-21 - CVE-2026-40244 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-40244

Vulnerability Analysis

This vulnerability represents a classic integer overflow condition in the OpenEXR library's DWA compression implementation. Specifically, the vulnerable code at internal_dwa_compressor.h:1722 performs a width-by-height multiplication (curc->width * curc->height) using 32-bit integer arithmetic without casting to size_t. When image dimensions are sufficiently large, this multiplication can wrap around the maximum value of a 32-bit signed integer, resulting in a much smaller value than expected.

The flaw is particularly notable because it follows the same overflow pattern that was addressed in CVE-2026-34589, indicating that this specific code location was overlooked during the previous remediation effort. The DWA compressor is a lossy compression algorithm commonly used for storing deep image data in EXR files.

Root Cause

The root cause is an integer overflow vulnerability (CWE-190) in the internal_dwa_compressor.h file at line 1722. The multiplication of width and height values for image buffers uses 32-bit signed integer arithmetic instead of proper size_t arithmetic. When the product of curc->width and curc->height exceeds INT32_MAX (2,147,483,647), the result wraps around to a negative or smaller positive value. This undersized value is then used for memory allocation or buffer operations, leading to heap buffer overflow conditions when the actual image data is written to the undersized buffer.

Attack Vector

The attack vector requires local access with user interaction—a victim must open a specially crafted EXR file. An attacker would create a malicious EXR file with image dimension metadata specifically chosen to trigger the integer overflow during DWA decompression. When a vulnerable application using OpenEXR processes this file:

1. The DWA decompressor reads the width and height values from the file
2. The multiplication at line 1722 overflows, producing a smaller-than-expected buffer size
3. Subsequent write operations overflow the undersized heap buffer
4. This heap corruption can potentially be leveraged for arbitrary code execution

Common attack scenarios include sending malicious EXR files via email, hosting them on file-sharing platforms, or injecting them into media production pipelines. Applications vulnerable include video editing software, 3D rendering applications, image viewers, and any software that uses OpenEXR for image processing.

Detection Methods for CVE-2026-40244

Indicators of Compromise

• Unexpected crashes in applications processing EXR files, particularly those with unusual or extremely large dimension metadata
• Memory corruption errors or heap-related crashes in processes using OpenEXR libraries
• EXR files with suspiciously large width or height values that approach or exceed integer overflow boundaries
• Application logs showing memory allocation failures followed by buffer overwrite attempts

Detection Strategies

• Monitor file processing applications for abnormal termination when handling EXR files
• Implement file integrity checking for EXR files entering production pipelines from external sources
• Deploy endpoint detection rules that flag EXR files with dimension metadata exceeding reasonable production limits
• Utilize memory protection technologies (ASLR, DEP/NX, CFI) to complicate exploitation attempts

Monitoring Recommendations

• Enable crash dump collection and analysis for applications using OpenEXR to identify exploitation attempts
• Implement logging for EXR file metadata parsing, particularly dimension values, to identify anomalous files
• Monitor for unusual process behavior following EXR file opens, such as unexpected network connections or child process spawning
• Review application logs for memory allocation failures in image processing workflows

How to Mitigate CVE-2026-40244

Immediate Actions Required

• Upgrade OpenEXR to patched versions: 3.4.10, 3.3.10, or 3.2.8 depending on your current version branch
• Audit systems to identify all applications using OpenEXR libraries and prioritize updates for those processing external files
• Restrict processing of EXR files from untrusted sources until patches are applied
• Ensure exploit mitigation technologies (ASLR, DEP, stack canaries) are enabled on systems processing EXR files

Patch Information

The OpenEXR project has released patched versions that address the integer overflow at internal_dwa_compressor.h:1722 by adding proper size_t casting before the multiplication operation. Users should upgrade to the following versions:

• Version 3.4.10 for users on the 3.4.x branch - GitHub Release v3.4.10
• Version 3.3.10 for users on the 3.3.x branch - GitHub Release v3.3.10
• Version 3.2.8 for users on the 3.2.x branch - GitHub Release v3.2.8

For detailed information about this vulnerability, refer to the GitHub Security Advisory GHSA-j526-66f6-fxhx.

Workarounds

• Implement input validation at the application level to reject EXR files with dimensions exceeding reasonable thresholds before OpenEXR processes them
• Use sandboxing or containerization for applications that must process untrusted EXR files to limit the impact of potential exploitation
• Disable DWA compression support if your workflow does not require it and your application provides configuration options
• Deploy file filtering at network boundaries to quarantine EXR files from untrusted sources pending security review