CVE-2026-40250: OpenEXR Buffer Overflow Vulnerability

CVE-2026-40250 Overview

CVE-2026-40250 is an Integer Overflow vulnerability affecting OpenEXR, the specification and reference implementation of the EXR file format widely used in the motion picture industry for high dynamic range image storage. The vulnerability exists in the DWA (DreamWorks Animation) compressor component, specifically at internal_dwa_compressor.h:1040, where an arithmetic operation is performed without proper type casting.

The flaw involves the calculation chan->width * chan->bytes_per_element being performed in int32 arithmetic without a (size_t) cast. This is the same overflow pattern that was previously addressed in other decoders through CVE-2026-34589, CVE-2026-34588, and CVE-2026-34544, but this particular line was missed during those remediation efforts.

Critical Impact

An attacker could craft a malicious EXR file that, when processed, triggers an integer overflow leading to potential memory corruption, arbitrary code execution, or application crashes in software utilizing affected OpenEXR versions.

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-2026-40250 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-40250

Vulnerability Analysis

This vulnerability represents a classic integer overflow condition (CWE-190) that occurs during image decompression operations. When processing EXR files using the DWA compression algorithm, the code calculates buffer sizes by multiplying channel width by bytes per element. Without proper type casting to size_t, this multiplication can overflow on 32-bit signed integers when processing images with large dimensions.

The integer overflow can result in the allocation of an undersized buffer, leading to subsequent out-of-bounds memory operations. This is particularly dangerous as the vulnerability requires user interaction—specifically opening a maliciously crafted EXR file—but once triggered, can lead to full compromise of the affected application's memory space.

The attack requires local access to deliver the malicious file to the target system. No authentication is required to exploit this vulnerability, and successful exploitation can result in high impacts to confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause is an improper integer type handling in the DWA compressor implementation. At line 1040 of internal_dwa_compressor.h, the multiplication operation chan->width * chan->bytes_per_element uses 32-bit signed integer arithmetic. When processing images with sufficiently large dimensions, this calculation can exceed the maximum value representable in an int32, causing the value to wrap around to a small or negative number.

The fix requires casting one of the operands to size_t before the multiplication, ensuring the arithmetic is performed using an unsigned integer type large enough to hold the result on the target platform. This is the same pattern that was applied in previous related CVEs (CVE-2026-34589, CVE-2026-34588, CVE-2026-34544) but was inadvertently missed for this specific code location.

Attack Vector

This vulnerability has a local attack vector, meaning an attacker must deliver a crafted EXR file to the target system. Common attack scenarios include:

The attacker creates a specially crafted EXR file with image dimension metadata designed to trigger the integer overflow during DWA decompression. When a user opens this file in any application utilizing vulnerable OpenEXR versions—such as professional VFX software, image editors, or media players—the overflow occurs during decompression, potentially leading to memory corruption and code execution in the context of the vulnerable application.

The vulnerability mechanism involves crafting an EXR file where the product of chan->width and chan->bytes_per_element exceeds INT32_MAX (2,147,483,647). When the overflow occurs, the resulting value wraps around, causing the allocator to reserve an insufficient buffer size. Subsequent write operations then corrupt adjacent memory regions. See the GitHub Security Advisory for additional technical details.

Detection Methods for CVE-2026-40250

Indicators of Compromise

• Presence of unusually large or malformed EXR files with abnormal dimension metadata values
• Application crashes or unexpected termination when processing EXR files
• Memory corruption errors or segmentation faults in processes handling EXR content
• Unusual process behavior following EXR file operations, potentially indicating code execution

Detection Strategies

• Monitor for application crashes or exceptions in software known to process EXR files (VFX applications, compositing software, image converters)
• Implement file integrity monitoring for unexpected EXR files appearing in processing directories
• Deploy endpoint detection rules to identify abnormal memory allocation patterns during image processing operations
• Use static analysis tools to scan for OpenEXR library versions matching vulnerable ranges (3.4.0-3.4.9, 3.3.0-3.3.9, 3.2.0-3.2.7)

Monitoring Recommendations

• Enable crash dump collection and analysis for applications processing EXR content to identify potential exploitation attempts
• Implement network traffic inspection for EXR files being downloaded or transferred, particularly from untrusted sources
• Monitor system logs for memory allocation failures or unusual behavior in image processing pipelines
• Track software inventory to maintain awareness of which systems have vulnerable OpenEXR versions deployed

How to Mitigate CVE-2026-40250

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 all systems and applications that depend on OpenEXR libraries to identify vulnerable installations
• Implement file validation procedures to quarantine EXR files from untrusted sources until systems are patched
• Consider temporarily disabling DWA decompression support if patching cannot be immediately performed

Patch Information

The OpenEXR project has released patched versions that address the integer overflow in internal_dwa_compressor.h:1040:

• 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

The fix applies a (size_t) cast to the multiplication operation, ensuring the arithmetic is performed in a type large enough to prevent overflow on the target platform.

Workarounds

• Restrict EXR file processing to files from trusted sources only until patches can be applied
• Implement sandboxing or containerization for applications that process untrusted EXR files to limit potential impact
• Use alternative compression methods (non-DWA) for EXR files where possible, as this specific vulnerability is in the DWA compressor
• Deploy application-level controls to reject EXR files with suspicious dimension metadata before processing

# Verify OpenEXR version to check vulnerability status
pkg-config --modversion OpenEXR

# For systems using the library, check linked version
ldd /path/to/application | grep -i openexr

# Update OpenEXR via package manager (example for systems with updated packages)
# Debian/Ubuntu:
sudo apt update && sudo apt install libopenexr-dev

# Or build from source with patched version
git clone https://github.com/AcademySoftwareFoundation/openexr.git
cd openexr
git checkout v3.4.10
cmake -B build -DCMAKE_INSTALL_PREFIX=/usr/local
cmake --build build
sudo cmake --install build