Vulnerability-Lookup

GHSA-6H6Q-9MWG-R6X7

Vulnerability from github – Published: 2026-07-24 18:31 – Updated: 2026-07-24 18:31

Details

libssh2 through 1.11.1, fixed in commit a13bb6c, contains a missing bounds check vulnerability that allows a malicious SSH server to trigger an arbitrary-length heap out-of-bounds read and a free of an uninitialized pointer via the publickey subsystem. In libssh2_publickey_list_fetch(), the version 1 response parser reads a server-controlled comment_len value and advances the parse pointer without verifying sufficient bytes remain in the buffer, causing the out-of-bounds read to leak heap pointers from adjacent allocations defeating ASLR, followed by heap allocator state corruption when the error cleanup path frees an uninitialized pointer from a non-zeroed realloc() region.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

7.7 (High)


                  
                    CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

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JSON

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{
  "affected": [],
  "aliases": [
    "CVE-2026-66034"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-125"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-24T17:17:35Z",
    "severity": "HIGH"
  },
  "details": "libssh2 through 1.11.1, fixed in commit a13bb6c, contains a missing bounds check vulnerability that allows a malicious SSH server to trigger an arbitrary-length heap out-of-bounds read and a free of an uninitialized pointer via the publickey subsystem. In libssh2_publickey_list_fetch(), the version 1 response parser reads a server-controlled comment_len value and advances the parse pointer without verifying sufficient bytes remain in the buffer, causing the out-of-bounds read to leak heap pointers from adjacent allocations defeating ASLR, followed by heap allocator state corruption when the error cleanup path frees an uninitialized pointer from a non-zeroed realloc() region.",
  "id": "GHSA-6h6q-9mwg-r6x7",
  "modified": "2026-07-24T18:31:30Z",
  "published": "2026-07-24T18:31:30Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-66034"
    },
    {
      "type": "WEB",
      "url": "https://github.com/libssh2/libssh2/pull/2202"
    },
    {
      "type": "WEB",
      "url": "https://github.com/libssh2/libssh2/commit/a13bb6c773f0d55ad1628cede57e99803cd898d9"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/libssh2-heap-out-of-bounds-read-via-publickey-subsystem"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

CVE-2026-66034 (GCVE-0-2026-66034)

Vulnerability from cvelistv5 – Published: 2026-07-24 16:42 – Updated: 2026-07-25 10:30 X_Open Source

Title

libssh2 Heap Out-of-Bounds Read via publickey subsystem

Summary

Severity

7.7 (High)


                        
                          CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

SSVC

Exploitation: none Automatable: no Technical Impact: total

CISA Coordinator (v2.0.3)

CWE

CWE-125 - Out-of-bounds Read
CWE-908 - Use of Uninitialized Resource

Assigner

VulnCheck

References

3 references

URL	Tags
https://github.com/libssh2/libssh2/pull/2202	issue-trackingpatch
https://github.com/libssh2/libssh2/commit/a13bb6c…	patch
https://www.vulncheck.com/advisories/libssh2-heap…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version
libssh2	libssh2	Affected: 0 , ≤ 1.11.1 (semver) Unaffected: a13bb6c773f0d55ad1628cede57e99803cd898d9 (git)

Date Public

2026-07-04 00:00

Credits

VladimirEliTokarev

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-66034",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-07-24T00:00:00+00:00",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-07-25T03:55:51.727Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "affected",
          "packageURL": "pkg:github/libssh2/libssh2",
          "product": "libssh2",
          "repo": "https://github.com/libssh2/libssh2",
          "vendor": "libssh2",
          "versions": [
            {
              "lessThanOrEqual": "1.11.1",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "a13bb6c773f0d55ad1628cede57e99803cd898d9",
              "versionType": "git"
            }
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        }
      ],
      "credits": [
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          "lang": "en",
          "type": "finder",
          "value": "VladimirEliTokarev"
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      "datePublic": "2026-07-04T00:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "value": "libssh2 through 1.11.1, fixed in commit a13bb6c, contains a missing bounds check vulnerability that allows a malicious SSH server to trigger an arbitrary-length heap out-of-bounds read and a free of an uninitialized pointer via the publickey subsystem. In libssh2_publickey_list_fetch(), the version 1 response parser reads a server-controlled comment_len value and advances the parse pointer without verifying sufficient bytes remain in the buffer, causing the out-of-bounds read to leak heap pointers from adjacent allocations defeating ASLR, followed by heap allocator state corruption when the error cleanup path frees an uninitialized pointer from a non-zeroed realloc() region."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "Automatable": "NOT_DEFINED",
            "Recovery": "NOT_DEFINED",
            "Safety": "NOT_DEFINED",
            "attackComplexity": "HIGH",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 7.7,
            "baseSeverity": "HIGH",
            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "NOT_DEFINED",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "PASSIVE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "HIGH",
            "vulnIntegrityImpact": "HIGH",
            "vulnerabilityResponseEffort": "NOT_DEFINED"
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          "format": "CVSS",
          "scenarios": [
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            "availabilityImpact": "HIGH",
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            "confidentialityImpact": "HIGH",
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            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
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      "problemTypes": [
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          "descriptions": [
            {
              "cweId": "CWE-125",
              "description": "Out-of-bounds Read",
              "lang": "en",
              "type": "CWE"
            },
            {
              "cweId": "CWE-908",
              "description": "Use of Uninitialized Resource",
              "lang": "en",
              "type": "CWE"
            }
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      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-25T10:30:09.019Z",
        "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
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      },
      "references": [
        {
          "name": "Pull Request",
          "tags": [
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          "url": "https://github.com/libssh2/libssh2/pull/2202"
        },
        {
          "name": "Patch Commit",
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        },
        {
          "tags": [
            "third-party-advisory"
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          "url": "https://www.vulncheck.com/advisories/libssh2-heap-out-of-bounds-read-via-publickey-subsystem"
        }
      ],
      "source": {
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      "title": "libssh2 Heap Out-of-Bounds Read via publickey subsystem",
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  "cveMetadata": {
    "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
    "assignerShortName": "VulnCheck",
    "cveId": "CVE-2026-66034",
    "datePublished": "2026-07-24T16:42:18.764Z",
    "dateReserved": "2026-07-23T20:45:17.816Z",
    "dateUpdated": "2026-07-25T10:30:09.019Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

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.

Action not permitted

GHSA-6H6Q-9MWG-R6X7

CVE-2026-66034 (GCVE-0-2026-66034)

Tags

Sightings

Nomenclature