CVE-2026-55586
SumatraPDF: Heap out-of-bounds write in vendored CHMLib LZX Huffman table construction reachable from crafted CHM files
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | Medium6.6 | CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L |
| NVDNVD · Deferred | 3.1 | Medium6.6 | CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L |
- EPSS (exploitation in 30 days)
- 0.17% · top 93% of all CVEs (6 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.6.
Weakness
Affected products
- affected <= 3.6.1rel
References (2)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-55586)Record last updated .