OpenEXR DWA Lossy Decoder Heap Out-of-Bounds Write Vulnerability

A heap out-of-bounds write vulnerability has been identified in the DWA lossy decoder of OpenEXR versions 3.2.0-3.2.6, 3.3.0-3.3.8, and 3.4.0-3.4.8. The vulnerability stems from an integer overflow in the calculation of per-component block pointers within the internal_dwa_decoder.h file. When processing a DWAA compressed image with a large width, the multiplication of numBlocksX * 64 overflows a signed 32-bit integer, resulting in a wrapped pointer. This wrapped pointer is then used in subsequent decoder operations, leading to out-of-bounds memory access during the lossy DCT execution path. This can be triggered using the exrcheck tool, impacting systems where OpenEXR is used to process image files.

Attack Chain

1. An attacker crafts a malicious OpenEXR image file with DWAA compression and a large image width.
2. The victim uses the exrcheck tool or an application linked against a vulnerable OpenEXR library to process the image.
3. The InputFile or ScanLineInputFile class initiates the image decoding process.
4. The exr_decoding_run function is called, which in turn calls exr_uncompress_chunk.
5. exr_uncompress_chunk calls internal_exr_undo_dwaa to decompress the DWAA data.
6. internal_exr_undo_dwaa invokes DwaCompressor_uncompress.
7. Inside DwaCompressor_uncompress, LossyDctDecoder_execute is called, triggering the integer overflow when calculating rowBlock pointers in internal_dwa_decoder.h.
8. LossyDctDecoder_execute attempts to write data to an out-of-bounds memory location, resulting in a crash (SEGV).

Impact

Successful exploitation of this vulnerability leads to a denial-of-service condition due to a write-side crash, as observed in the LossyDctDecoder_execute function. The vulnerability affects applications that utilize the OpenEXR library to process DWAA compressed images. While the source doesn’t specify the number of victims or targeted sectors, any system processing untrusted OpenEXR images with affected versions is at risk. This could impact image editing software, rendering pipelines, and other applications that rely on OpenEXR.

Recommendation

• Upgrade OpenEXR to versions 3.2.7, 3.3.9, or 3.4.9 or later to patch CVE-2026-34589.
• Deploy the Sigma rule “Detect exrcheck crash” to identify instances where the exrcheck tool crashes due to this vulnerability.
• Monitor systems for abnormal program termination signals (e.g., SEGV) originating from OpenEXR libraries during image processing, as these may indicate exploitation attempts.
• Block downloads from the URL https://github.com/user-attachments/files/26318786/dwa_scanline_exrcheck.zip to prevent users from downloading a known malicious test case.