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OpenEXR has a signed 32-bit Overflow in PIZ Decoder Leads to OOB Read/Write

High severity GitHub Reviewed Published Apr 5, 2026 in AcademySoftwareFoundation/openexr

Package

pip OpenEXR (pip)

Affected versions

>= 3.1.0, < 3.2.7
>= 3.3.0, < 3.3.9
>= 3.4.0, < 3.4.9

Patched versions

3.2.7
3.3.9
3.4.9

Description

Summary

internal_exr_undo_piz() advances the working wavelet pointer with signed 32-bit arithmetic:

wavbuf += nx * ny * wcount;

Because nx, ny, and wcount are int, a crafted EXR file can make this product overflow and wrap. The next channel then decodes from an incorrect address. The wavelet decode path operates in place, so this yields both out-of-bounds reads and out-of-bounds writes.

Tested on commit 7820b7e1b93405ba1d551c43a945018226b75bc5

Technical Details

The vulnerable decode path is:

  1. internal_exr_undo_piz() sets wavbuf = decode->scratch_buffer_1.
  2. For each channel, it calls wav_2D_decode (wavbuf + j, ...).
  3. It then advances wavbuf with wavbuf += nx * ny * wcount.

The overflow happens in step 3. Once wavbuf is wrapped, the next channel's wavelet decode runs on the wrong address.

In the 14-bit wavelet path, wdec14_4() first reads:

  • *px
  • *p10
  • *p01
  • *p11

and then writes back to the same locations:

  • *px = ...
  • *p01 = ...
  • *p10 = ...
  • *p11 = ...

As a result, the bug is not just a crash-only invalid read. It is an out-of-bounds read/write condition.

Reproduction

piz_scanline_redzone.zip

Build exrcheck with ASAN and run:

❯ ./build-asan/bin/exrcheck /tmp/piz_scanline_redzone.exr
 file /tmp/piz_scanline_redzone.exr /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_piz.c:373:19: runtime error: signed integer overflow: 134217724 * 32 cannot be represented in type 'int'
=================================================================
==1711239==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7bedc3934700 at pc 0x7bf1f100f498 bp 0x7ffe032d8f00 sp 0x7ffe032d8ef0
READ of size 2 at 0x7bedc3934700 thread T0
    #0 0x7bf1f100f497 in wdec14_4 /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_piz.c:148
    #1 0x7bf1f100f497 in wav_2D_decode /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_piz.c:403
    #2 0x7bf1f100f497 in internal_exr_undo_piz /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_piz.c:727
    #3 0x7bf1f115b038 in exr_uncompress_chunk /home/pop/sec/openexr/src/lib/OpenEXRCore/compression.c:546
    #4 0x7bf1f1161168 in exr_decoding_run /home/pop/sec/openexr/src/lib/OpenEXRCore/decoding.c:580
    #5 0x7bf1f2a71add in run_decode /home/pop/sec/openexr/src/lib/OpenEXR/ImfScanLineInputFile.cpp:586
    #6 0x7bf1f2a83dc4 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 0x7bf1f28c6a81 in Imf_4_0::InputFile::Data::readPixels(int, int) /home/pop/sec/openexr/src/lib/OpenEXR/ImfInputFile.cpp:458
    #8 0x7bf1f3bfe2dc in readScanline<Imf_4_0::InputPart> /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:239
    #9 0x7bf1f3c05b04 in readMultiPart /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:905
    #10 0x7bf1f3c126fd in runChecks<char const*> /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:1171
    #11 0x7bf1f3c146b9 in Imf_4_0::checkOpenEXRFile(char const*, bool, bool, bool) /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:1835
    #12 0x5d9675fce8f8 in exrCheck(char const*, bool, bool, bool, bool) /home/pop/sec/openexr/src/bin/exrcheck/main.cpp:96
    #13 0x5d9675fcb2b1 in main /home/pop/sec/openexr/src/bin/exrcheck/main.cpp:164
    #14 0x7bf1efe2a1c9 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #15 0x7bf1efe2a28a in __libc_start_main_impl ../csu/libc-start.c:360
    #16 0x5d9675fcc844 in _start (/home/pop/sec/openexr/build-asan/bin/exrcheck+0xe844) (BuildId: 087c972343a5372940c42c0a2e7bce4a84288aec)

0x7bedc3934700 is located 256 bytes before 8590720784-byte region [0x7bedc3934800,0x7befc39f4710)
allocated by thread T0 here:
    #0 0x7bf1f40fd9c7 in malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:69
    #1 0x7bf1f115883e in internal_decode_alloc_buffer /home/pop/sec/openexr/src/lib/OpenEXRCore/coding.c:256
    #2 0x7bf1f100da97 in internal_exr_undo_piz /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_piz.c:643
    #3 0x7bf1f115b038 in exr_uncompress_chunk /home/pop/sec/openexr/src/lib/OpenEXRCore/compression.c:546
    #4 0x7bf1f1161168 in exr_decoding_run /home/pop/sec/openexr/src/lib/OpenEXRCore/decoding.c:580
    #5 0x7bf1f2a71add in run_decode /home/pop/sec/openexr/src/lib/OpenEXR/ImfScanLineInputFile.cpp:586
    #6 0x7bf1f2a83dc4 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 0x7bf1f28c6a81 in Imf_4_0::InputFile::Data::readPixels(int, int) /home/pop/sec/openexr/src/lib/OpenEXR/ImfInputFile.cpp:458
    #8 0x7bf1f3bfe2dc in readScanline<Imf_4_0::InputPart> /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:239
    #9 0x7bf1f3c05b04 in readMultiPart /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:905
    #10 0x7bf1f3c126fd in runChecks<char const*> /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:1171
    #11 0x7bf1f3c146b9 in Imf_4_0::checkOpenEXRFile(char const*, bool, bool, bool) /home/pop/sec/openexr/src/lib/OpenEXRUtil/ImfCheckFile.cpp:1835
    #12 0x5d9675fce8f8 in exrCheck(char const*, bool, bool, bool, bool) /home/pop/sec/openexr/src/bin/exrcheck/main.cpp:96
    #13 0x5d9675fcb2b1 in main /home/pop/sec/openexr/src/bin/exrcheck/main.cpp:164
    #14 0x7bf1efe2a1c9 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #15 0x7bf1efe2a28a in __libc_start_main_impl ../csu/libc-start.c:360
    #16 0x5d9675fcc844 in _start (/home/pop/sec/openexr/build-asan/bin/exrcheck+0xe844) (BuildId: 087c972343a5372940c42c0a2e7bce4a84288aec)

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_piz.c:148 in wdec14_4
Shadow bytes around the buggy address:
  0x7bedc3934480: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x7bedc3934500: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x7bedc3934580: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x7bedc3934600: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x7bedc3934680: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x7bedc3934700:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x7bedc3934780: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x7bedc3934800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7bedc3934880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7bedc3934900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7bedc3934980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==1711239==ABORTING

To prove this is both READ and WRITE, we can also memcheck against non-ASAN release build:

valgrind --tool=memcheck --leak-check=no --track-origins=no \
  --error-limit=no --num-callers=20 \
  ./build-relwithdebinfo/bin/exrcheck /tmp/piz_scanline_redzone.exr

Observed result:

This confirms the bug is an OOB read/write, not only a read-first crash.

Redzone-Oriented File

  • width: 67108862
  • height: 32
  • channel A: FLOAT, sampling 1 x 1
  • channel B: HALF, sampling 33554431 x 16

This makes:

width * 32 * 2 = 4294967168

which wraps signed 32-bit arithmetic to -128.

That places the next wavbuf access just before the allocated buffer, producing a clean heap-overflow report.

Impact

A crafted EXR file can trigger out-of-bounds memory access during PIZ decompression. The primitive includes both invalid reads and invalid writes. Depending on allocator layout and surrounding memory, this could lead to process crash, memory corruption, or potentially stronger exploitation outcomes.

Recommended Fix

  • compute channel span in 64-bit arithmetic
  • reject any overflow in nx * ny * wcount
  • validate cumulative per-channel decoded footprint against outsz before wavelet decode
  • fail decompression if channel-derived layout does not exactly fit the decompression buffer

Found by: Quang Luong of Calif.io

References

@cary-ilm cary-ilm published to AcademySoftwareFoundation/openexr Apr 5, 2026
Published by the National Vulnerability Database Apr 6, 2026
Published to the GitHub Advisory Database Apr 8, 2026
Reviewed Apr 8, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Local
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(7th percentile)

Weaknesses

Out-of-bounds Read

The product reads data past the end, or before the beginning, of the intended buffer. Learn more on MITRE.

Integer Overflow or Wraparound

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number. Learn more on MITRE.

Out-of-bounds Write

The product writes data past the end, or before the beginning, of the intended buffer. Learn more on MITRE.

CVE ID

CVE-2026-34588

GHSA ID

GHSA-588r-cr5c-w6hf

Source code

Credits

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