CVE-2026-45696: OpenEXR HTJ2K decoder heap buffer over-read in ht_undo_impl() (DoS)

OpenEXR is the reference implementation and specification for the EXR image format, widely used in the motion picture industry. In versions 3.4.0 through 3.4.11, the HTJ2K (High-Throughput JPEG 2000) decoder, htundoimpl() in OpenEXRCore is vulnerable to a heap-buffer-overflow READ. The htundoimp function copies decoded pixels out of a per-line OpenJPH buffer using the EXR channel's declared width as the iteration count. The codestream embedded in the EXR chunk can declare different (smaller) tile/line dimensions than the EXR header advertises, but htundoimpl() does not validate this — it pulls width 32-bit samples from curline->i32[] without checking the OpenJPH line buffer's actual length. A crafted EXR file produces a 4-byte heap-buffer-overflow READ immediately after a buffer allocated by ojph::local::codestream::finalizealloc(). The bug is reachable through the standard scanline-decode entry point used by every consumer of exrdecodingrun/Imf::checkOpenEXRFile, including thumbnailers, asset pipelines, and the exrcheck utility — i.e. any application that opens untrusted EXR files. The result is a deterministic crash (DoS) and potential adjacent-heap leak. This issue has been fixed in version 3.4.12.