CVE-2026-55586 (GCVE-0-2026-55586)

Vulnerability from cvelistv5 – Published: 2026-08-20 16:35 – Updated: 2026-08-21 21:47
VLAI
Title
SumatraPDF: Heap out-of-bounds write in vendored CHMLib LZX Huffman table construction reachable from crafted CHM files
Summary
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.
Severity
6.6 (Medium)
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-21 20:58 UTC
CWE
  • CWE-119 - Improper Restriction of Operations within the Bounds of a Memory Buffer
  • CWE-787 - Out-of-bounds Write
Assigner
GitHub_M CNA under the mitre root
CNA scorecard C 72/100 over 7618 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
sumatrapdfreader sumatrapdf Affected: <= 3.6.1rel
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

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