Sign in
Deutsch English Español Polski
High

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

  • Disclosed: 08.04.2026
  • Updated: 11.10.2026 14:18

Summary

The DWA lossy decoder constructs temporary per-component block pointers using signed 32-bit arithmetic. For a large enough width, the calculation overflows and later decoder stores operate on a wrapped pointer outside the allocated rowBlock backing store.

This bug is reachable from the public decoder path and can be reproduced through the shipped exrcheck tool with a crafted scanline DWAA file. The confirmed dynamic symptom is a write-side crash in the lossy DCT execution path.

Tested on commit: 7820b7e1b93405ba1d551c43a945018226b75bc5

Root Cause and Data Flow

The vulnerable pointer construction lives in src/lib/OpenEXRCore/internal_dwa_decoder.h:

c
for (int comp = 1; comp < numComp; ++comp)
    rowBlock[comp] = rowBlock[comp - 1] + numBlocksX * 64;

The expression numBlocksX * 64 is computed as signed int. Once numBlocksX is large enough, the multiplication wraps, and rowBlock[comp] points backward rather than forward into the temporary decode buffer.

Later, LossyDctDecoder_execute() uses those derived pointers for real loads and stores during the block shuffle and reconstruction process. At that point the decoder is no longer operating within the bounds of the allocation created for rowBlockHandle.

The public control flow is the standard one:

c
InputFile / ScanLineInputFile public read
  -> exr_decoding_run(...)
     -> exr_uncompress_chunk(...)
        -> internal_exr_undo_dwaa(...)
           -> DwaCompressor_uncompress(...)
              -> LossyDctDecoder_execute(...)

UBSan gives a clean root-cause diagnosis on the overflowing multiply, while ASAN shows the later memory error in the write-side decode path.

Reproduction

dwa_scanline_exrcheck.zip

Build with exrcheck with ASAN and run:

❯ ./build-asan/bin/exrcheck /tmp/dwa_scanline_exrcheck.exr
 file /tmp/dwa_scanline_exrcheck.exr /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_dwa_decoder.h:331:58: runtime error: signed integer overflow: 33554432 * 64 cannot be represented in type 'int'
AddressSanitizer:DEADLYSIGNAL
=================================================================
==1684058==ERROR: AddressSanitizer: SEGV on unknown address 0x758f8e5f0800 (pc 0x75979e850336 bp 0x7ffe8f1d3420 sp 0x7ffe8f1d30f0 T0)
==1684058==The signal is caused by a WRITE memory access.
    #0 0x75979e850336 in LossyDctDecoder_execute /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_dwa_decoder.h:524
    #1 0x75979e879592 in DwaCompressor_uncompress /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_dwa_compressor.h:1210
    #2 0x75979e879592 in internal_exr_undo_dwaa /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_dwa.c:231
    #3 0x75979e95f878 in exr_uncompress_chunk /home/pop/sec/openexr/src/lib/OpenEXRCore/compression.c:542
    #4 0x75979e9659a8 in exr_decoding_run /home/pop/sec/openexr/src/lib/OpenEXRCore/decoding.c:580
    #5 0x7597a0271add in run_decode /home/pop/sec/openexr/src/lib/OpenEXR/ImfScanLineInputFile.cpp:586
    #6 0x7597a0283dc4 in Imf_4_0::ScanLineInputFile::Data::readPixels(Imf_4_0::FrameBuffer const&, int, int) /home/pop/sec/openexr/src/lib/OpenEXR/ImfScanLineInputFile.cpp:500
    #7 0x7597a00c6a81 in Imf_4_0::InputFile::Data::readPixels(int, int) /home/pop/sec/openexr/src/lib/OpenEXR/ImfInputFile.cpp:458
    #8 0x7597a13fe2dc in readScanline<Imf_4_0::InputPart> /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:239
    #9 0x7597a1405b04 in readMultiPart /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:905
    #10 0x7597a14126fd in runChecks<char const*> /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:1171
    #11 0x7597a14146b9 in Imf_4_0::checkOpenEXRFile(char const*, bool, bool, bool) /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:1835
    #12 0x61ba9582b8f8 in exrCheck(char const*, bool, bool, bool, bool) /home/pop/sec/openexr/src/bin/exrcheck/main.cpp:96
    #13 0x61ba958282b1 in main /home/pop/sec/openexr/src/bin/exrcheck/main.cpp:164
    #14 0x75979d62a1c9 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #15 0x75979d62a28a in __libc_start_main_impl ../csu/libc-start.c:360
    #16 0x61ba95829844 in _start (/home/pop/sec/openexr/build-asan/bin/exrcheck+0xe844) (BuildId: 087c972343a5372940c42c0a2e7bce4a84288aec)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_dwa_decoder.h:524 in LossyDctDecoder_execute
==1684058==ABORTING

Found by: Quang Luong of Calif.io

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Python (PyPI) openexr >= 3.2.0, < 3.2.7, >= 3.3.0, < 3.3.9, >= 3.4.0, < 3.4.9 3.2.7, 3.3.9, 3.4.9

References

CVSS score 5/10
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
Weakness (CWE)
CWE-190, CWE-787
Platform
Python (PyPI)
Package
openexr
Disclosed
08.04.2026
Updated
11.10.2026 14:18

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2026-2848 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-p8xc-w3q4-h64x - CC BY 4.0

Vulnerability history: openexr

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (15) in the archive
Total entries
15
First → latest
05.2022 04.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • High 7
  • Medium 7
  • Low 1

Disclosures per year

Severity:
  1. OpenEXR: DWA Lossy Decoder Heap Out-of-Bounds Write this entry
    High · 5.0 CVE-2026-34589 >= 3.2.0, < 3.2.7, >= 3.3.0, < 3.3.9, >= 3.4.0, < 3.4.9 3.2.7, 3.3.9, 3.4.9
  2. OpenEXR has a signed 32-bit Overflow in PIZ Decoder Leads to OOB Read/Write
    High · 7.8 CVE-2026-34588 >= 3.1.0, < 3.2.7, >= 3.3.0, < 3.3.9, >= 3.4.0, < 3.4.9 3.2.7, 3.3.9, 3.4.9
  3. OpenEXR: Heap information disclosure in PXR24 decompression via unchecked decompressed size (undo_pxr24_impl)
    High CVE-2026-34543 >= 3.4.0, < 3.4.8, >= 3.3.0, <= 3.3.8, >= 3.2.0, <= 3.2.6 3.4.8
  4. OpenEXR: integer overflow to OOB write in uncompress_b44_impl()
    High CVE-2026-34544 >= 3.4.0, < 3.4.8, >= 3.3.0, <= 3.3.8, >= 3.2.0, <= 3.2.6 3.4.8
  5. OpenEXR's CompositeDeepScanLine integer-overflow leads to heap OOB write
    High CVE-2026-27622 >= 2.3.0, < 3.2.6, >= 3.3.0, < 3.3.8, >= 3.4.0, < 3.4.6 3.2.6, 3.3.8, 3.4.6
  6. OpenEXR Heap-Based Buffer Overflow in Deep Scanline Parsing via Forged Unpacked Size
    High · 7.8 CVE-2025-48071 >= 3.3.0, < 3.3.3 3.3.3
  7. OpenEXR invalid write
    High · 8.8 CVE-2017-9111 < 2.2.1 2.2.1

Know which vulnerabilities affect your application

With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.

Connect your application
DockRay newsletter

Application security in your inbox

Important vulnerabilities, actionable guidance and practical advice for your applications. Choose your technologies and follow what matters to your project.

  • A daily digest of new vulnerabilities, critical ones included.
  • Notifications about important updates.
  • Practical advice on application security and monitoring.

Leave empty to receive updates for every technology.

Privacy policy

Free to subscribe. Unsubscribe with one click in any email.