OpenEXR provides the specification and reference implementation of the EXR file format, an image storage format for the motion picture industry. Versions 3.4.0 through 3.4.9 have a signed integer overflow vulnerability in OpenEXRs HTJ2K (High-Throughput JPEG 2000) decompression path. The ht_undo_impl() function in src/lib/OpenEXRCore/internal_ht.cpp accumulates a bytes-per-line value (bpl) using a 32-bit signed integer with no overflow guard. A crafted EXR file with 16,385 FLOAT channels at the HTJ2K maximum width of 32,767 causes bpl to overflow INT_MAX, producing undefined behavior confirmed by UBSan. On an
allocator-permissive host where the required ~64 GB allocation succeeds, the wrapped negative bpl value would subsequently be used as a per-scanline pointer advance, which would produce a heap out-of-bounds write. On a memory-constrained host, the allocation fails before ht_undo_impl() is entered. This is the second distinct integer overflow in ht_undo_impl(). CVE-2026-34545 addressed a different overflow in the same function — the int16_t p pixel-loop counter at line ~302 that overflows when iterating over channels whose width exceeds 32,767. The CVE-2026-34545 fix did not touch the int bpl accumulator at line 211, which is the subject of this advisory. The bpl accumulator was also not addressed by any of the 8 advisories in the 2026-04-05 v3.4.9 release batch. This finding is structurally identical to CVE-2026-34588 (PIZ wcount*nx overflow in internal_piz.c) and should be remediated with the same pattern. The CVE-2026-34588 fix did not touch internal_ht.cpp. Version 3.4.10 contains a remediation that addresses the vulnerability in internal_ht.cpp.
Weakness
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.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Openexr | Openexr | 3.4.0 (including) | 3.4.10 (excluding) |
| Openexr | Ubuntu | devel | * |
| Openexr | Ubuntu | upstream | * |
Potential Mitigations
- Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
- If possible, choose a language or compiler that performs automatic bounds checking.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
- Use libraries or frameworks that make it easier to handle numbers without unexpected consequences.
- Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++). [REF-106]
- Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
- Use unsigned integers where possible. This makes it easier to perform validation for integer overflows. When signed integers are required, ensure that the range check includes minimum values as well as maximum values.
- Understand the programming language’s underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, “not-a-number” calculations, and how the language handles numbers that are too large or too small for its underlying representation. [REF-7]
- Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.