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CVE-2026-55586

6.6 · MEDIUM

SumatraPDF is a multi-format reader for Windows.

Published Aug 20, 2026CWE-119EPSS 0.17%

Overview

CVE-2026-55586 is a medium-severity vulnerability. It was published on August 20, 2026 and has a CVSS 3.1 base score of 6.6 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 6.6, rated MEDIUM. It requires local or adjacent network access to exploit. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/sumatrapdfreader/sumatrapdf/commit/13b3d4204dd12d93d426f2157b157b149edc29bfGitHubgithub.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-m423-rp8p-whj8

How CyberStrike helps

Frequently asked questions

What is CVE-2026-55586?

CVE-2026-55586 is a medium-severity vulnerability. It was published on August 20, 2026 and has a CVSS 3.1 base score of 6.6 (MEDIUM).

How severe is CVE-2026-55586?

This vulnerability has a CVSS 3.1 base score of 6.6, rated MEDIUM. It requires local or adjacent network access to exploit. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-55586?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-55586?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-55586 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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