CVE-2026-55586
SumatraPDF is a multi-format reader for Windows. In 3.6.1 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.
- CVSS 3.1
- 6.6
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L - EPSS
- 0.2% chance of exploitation in the next 30 days; higher than 6% of CVEs (scores of 2026-10-25)
- CWEs
- CWE-119, CWE-787
- Published
- Modified
- Record from
- the NVD, synced