CVE-2026-55586 - SumatraPDF: Heap out-of-bounds write in vendored CHMLib LZX Huffman table construction reachable from crafted CHM files
Brief
CVE ID : CVE-2026-55586
Published : Aug. 20, 2026, 4:35 p. m.
- 34 minutes ago
Description : SumatraPDF is a multi-format reader for Windows. In 3.
- 1 and earlier, a crafted CHM file can supply malformed LZX Huffman code lengths to make_decode_table in ext/CHMLib/lzx. c. In the long-code branch, the function writes new internal nodes through next_symbol before validating that the canonical Huffman table has overflowed.
The PRETREE case can write beyond the 104-entry PRETREE_table into adjacent heap state in struct LZXstate when reached through chm_open, chm_retrieve_object, LZXdecompress, and BUILD_TABLE. This produces heap memory corruption in the parser process, while arbitrary code execution has not been demonstrated. No fixed version is available as of this review.