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 v3 6.6 MEDIUM

6.6^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 1.8 / Impact : 4.7

Attack Vector LOCAL

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact LOW

Integrity Impact HIGH

Availability Impact LOW

Scope UNCHANGED

References

Link	Resource
https://github.com/sumatrapdfreader/sumatrapdf/commit/13b3d4204dd12d93d426f2157b157b149edc29bf
https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-m423-rp8p-whj8

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-20 17:18

Updated : 2026-08-21 22:16

NVD link : CVE-2026-55586

Mitre link : CVE-2026-55586

CVE.ORG link : CVE-2026-55586

JSON object : View

Products Affected

No product.

CWE

CWE-119

Improper Restriction of Operations within the Bounds of a Memory Buffer

CWE-787

Out-of-bounds Write

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