OpenEXR: Heap out-of-bounds write in exrmultiview with subsampled channel union

OpenEXR is the reference implementation and specification for the EXR image format, widely used in the motion picture industry. In versions before 3.2.11, 3.3.0 through 3.3.12, and 3.4.0 through 3.4.13, exrmultiview can write past a heap allocation when it combines two attacker-supplied, individually valid scanline EXR files whose union dataWindow is not aligned to one view's channel subsampling. The utility allocates sampled channel storage using a truncated union_width / xSampling, then reads the sampled input through a Slice based on the misaligned union window, producing a heap out-of-bounds write. The trigger is normal public-tool processing, such as exrmultiview left A.exr right B.exr out.exr with crafted but valid inputs, so this is not solely an API or caller-precondition issue. This issue is fixed in versions 3.2.11, 3.3.13, and 3.4.14.

A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().

An attacker operating through local access may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.