Vulnerability-Lookup

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

Vulnerability from cvelistv5 – Published: 2026-08-20 16:35 – Updated: 2026-08-21 21:47

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 mitre root

References

2 references

URL	Tags
https://github.com/sumatrapdfreader/sumatrapdf/se…	x_refsource_CONFIRM
https://github.com/sumatrapdfreader/sumatrapdf/co…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
sumatrapdfreader	sumatrapdf	Affected: <= 3.6.1rel	guessed

Show details on NVD website

JSON

To clipboard

{
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        "metrics": [
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              "content": {
                "id": "CVE-2026-55586",
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                    "Automatable": "no"
                  },
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                    "Technical Impact": "partial"
                  }
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                "role": "CISA Coordinator",
                "timestamp": "2026-08-21T20:58:52.272523Z",
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            }
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      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
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            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "LOW",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
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            "userInteraction": "REQUIRED",
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          }
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      ],
      "problemTypes": [
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          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-787",
              "description": "CWE-787: Out-of-bounds Write",
              "lang": "en",
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          ]
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      ],
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        "shortName": "GitHub_M"
      },
      "references": [
        {
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          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-m423-rp8p-whj8"
        },
        {
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    }
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FKIE_CVE-2026-55586

Vulnerability from fkie_nvd - Published: 2026-08-20 17:18 - Updated: 2026-08-21 22:16

Severity

6.6 (Medium) - CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/sumatrapdfreader/sumatrapdf/commit/13b3d4204dd12d93d426f2157b157b149edc29bf
	security-advisories@github.com	https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-m423-rp8p-whj8

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "sumatrapdf",
          "vendor": "sumatrapdfreader",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c= 3.6.1rel"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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."
    }
  ],
  "id": "CVE-2026-55586",
  "lastModified": "2026-08-21T22:16:41.210",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "LOW",
          "baseScore": 6.6,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 4.7,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-55586",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-21T20:58:52.272523Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-20T17:18:27.723",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/sumatrapdfreader/sumatrapdf/commit/13b3d4204dd12d93d426f2157b157b149edc29bf"
    },
    {
      "source": "security-advisories@github.com",
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    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-119"
        },
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

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

FKIE_CVE-2026-55586

Tags

Sightings

Nomenclature