VULNERABILITY INTELLIGENCE
CVE-2026-55586
CVSS score6.6 MEDIUM
EPSS probability0.17%
CISA KEVNot currently listed
Published2026-08-20
Last modified2026-10-18
CVSS vectorCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L
Description
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.
Weakness classification
- security-advisories@github.com: CWE-119