CVE-2026-34380: OpenEXR Buffer Overflow Vulnerability

CVE-2026-34380 Overview

A signed integer overflow vulnerability exists in OpenEXR, the industry-standard image file format specification and reference implementation used extensively in the motion picture and visual effects industries. The vulnerability is located in the undo_pxr24_impl() function within src/lib/OpenEXRCore/internal_pxr24.c at line 377, where improper integer type handling during pixel width calculations can lead to a heap buffer overflow condition.

Critical Impact

Attackers can craft malicious EXR files that exploit the signed integer overflow to bypass bounds checking, potentially causing denial of service through memory corruption or enabling limited out-of-bounds write operations.

Affected Products

• OpenEXR versions 3.2.0 to before 3.2.7
• OpenEXR versions 3.3.0 to before 3.3.9
• OpenEXR versions 3.4.0 to before 3.4.9

Discovery Timeline

• 2026-04-06 - CVE CVE-2026-34380 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-34380

Vulnerability Analysis

The vulnerability stems from improper integer type handling during PXR24 decompression operations. In the undo_pxr24_impl() function, the expression (uint64_t)(w * 3) computes the multiplication of the width value w by 3 as a signed 32-bit integer before the cast to uint64_t occurs. This ordering is critical because when w contains a sufficiently large value, the multiplication w * 3 overflows the signed 32-bit integer representation before being promoted to the 64-bit unsigned type.

Under the C standard, signed integer overflow constitutes undefined behavior. However, on common build configurations using clang or gcc without sanitizers enabled, two's-complement wraparound typically occurs. For carefully selected values of w, this wraparound produces a small positive integer result. This artificially small value can then bypass subsequent bounds validation checks that were designed to prevent buffer overruns.

Once the bounds check is incorrectly passed, the PXR24 decoding loop proceeds with its normal operation, writing decompressed pixel data through the dout pointer. Because the bounds check was circumvented, these write operations can extend significantly beyond the boundaries of the allocated output buffer, resulting in heap corruption.

Root Cause

The root cause is a classic integer overflow vulnerability classified as CWE-190 (Integer Overflow or Wraparound). The vulnerable code performs signed 32-bit integer arithmetic before widening to an unsigned 64-bit type. The fix requires ensuring the multiplication is performed in a wider integer type from the outset, or validating the input width value against safe bounds before the arithmetic operation occurs.

Attack Vector

Exploitation requires an attacker to craft a malicious EXR image file with a specially chosen width value that triggers the integer overflow condition. When this file is processed by an application using a vulnerable version of OpenEXR, the PXR24 decompression routine is invoked. The crafted width value causes the signed multiplication to wrap around to a small positive number, bypassing the buffer size validation.

The attack requires network access to deliver the malicious file and user interaction to open or process it. Once the bounds check is bypassed, the decoder writes pixel data beyond the allocated heap buffer. This can corrupt adjacent heap metadata or application data structures, potentially leading to application crashes (denial of service) or, in certain memory layouts, limited controlled writes that could affect application integrity.

The vulnerability mechanism works as follows: when processing a malicious EXR file with a crafted width parameter, the undo_pxr24_impl() function computes w * 3 as a signed 32-bit operation. If w is sufficiently large (e.g., values approaching INT_MAX / 3), the result overflows and wraps to a small or negative value. After casting to uint64_t, a negative result becomes a very large positive number (which would fail bounds checks), but certain overflow points produce small positive values that pass validation, allowing the subsequent buffer overwrite.

Detection Methods for CVE-2026-34380

Indicators of Compromise

• Unexpected application crashes or segmentation faults when processing EXR image files
• Memory corruption errors in applications using OpenEXR libraries during image decoding operations
• EXR files with abnormally large or unusual dimension values in metadata headers
• Heap corruption patterns detected in process memory during EXR file handling

Detection Strategies

• Implement file validation to check EXR image dimension fields for unusually large or suspicious values before processing
• Deploy application-level monitoring to detect crashes specifically during EXR decompression operations
• Use AddressSanitizer (ASan) or similar memory safety tools in testing environments to catch buffer overflows during EXR processing
• Monitor for repeated failures in image processing pipelines that handle user-supplied EXR content

Monitoring Recommendations

• Enable heap corruption detection in applications that process untrusted EXR files from external sources
• Implement logging around OpenEXR library calls to capture dimension parameters for forensic analysis
• Consider sandboxing EXR processing operations to contain potential exploitation attempts
• Audit systems for vulnerable OpenEXR versions using software composition analysis tools

How to Mitigate CVE-2026-34380

Immediate Actions Required

• Upgrade OpenEXR to patched versions 3.2.7, 3.3.9, or 3.4.9 immediately for all production systems
• Audit all applications and dependencies that include OpenEXR libraries to identify vulnerable installations
• Temporarily disable processing of untrusted EXR files from external sources until patches are applied
• Review and update container images, virtual machine templates, and build pipelines that include OpenEXR

Patch Information

The OpenEXR project has released security patches addressing this vulnerability in three release branches. Users should upgrade to the appropriate fixed version based on their current deployment:

• OpenEXR v3.2.7 for the 3.2.x branch
• OpenEXR v3.3.9 for the 3.3.x branch
• OpenEXR v3.4.9 for the 3.4.x branch

Additional details are available in the GitHub Security Advisory GHSA-q3v8-hw4m-59w5.

Workarounds

• Restrict EXR file processing to trusted sources only until the library can be patched
• Implement input validation at the application level to reject EXR files with dimension values exceeding reasonable thresholds
• Build OpenEXR with compiler sanitizers (e.g., -fsanitize=signed-integer-overflow) to detect overflow conditions, though this may impact performance
• Use process isolation or containerization to limit the impact of potential exploitation during the interim patching period

# Verify OpenEXR version to check vulnerability status
pkg-config --modversion OpenEXR
# or check library directly
ldconfig -p | grep -i openexr

# Update OpenEXR on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade openexr libopenexr-dev

# For source builds, upgrade to fixed version
git clone https://github.com/AcademySoftwareFoundation/openexr.git
cd openexr
git checkout v3.4.9
mkdir build && cd build
cmake .. && make && sudo make install