{
  "id": "CVE-2026-66033",
  "url": "https://spydr.io/cve/CVE-2026-66033",
  "published": "2026-07-24T17:17:35.263Z",
  "modified": "2026-07-30T15:44:47.257Z",
  "score": 8.7,
  "severity": "high",
  "cvss_version": "4.0",
  "vector": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/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",
  "score_source": "vulncheck.com",
  "epss": 0.00695,
  "epss_percentile": 0.51318,
  "exploited": false,
  "kev": null,
  "ssvc_exploitation": "none",
  "vendors": [
    "libssh2"
  ],
  "products": [
    "libssh2"
  ],
  "cwes": [
    "CWE-125",
    "CWE-191"
  ],
  "description": "libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.",
  "status": "Analyzed",
  "score_type": "Secondary",
  "scores": {
    "cvss_v40": 8.7,
    "cvss_v31": 7.5,
    "cvss_v30": null
  },
  "references": [
    {
      "url": "https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6",
      "tags": [
        "Patch"
      ]
    },
    {
      "url": "https://github.com/libssh2/libssh2/pull/2401",
      "tags": [
        "Issue Tracking",
        "Patch"
      ]
    },
    {
      "url": "https://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation",
      "tags": [
        "Patch",
        "Third Party Advisory"
      ]
    }
  ],
  "nvd_url": "https://nvd.nist.gov/vuln/detail/CVE-2026-66033",
  "covered_in": [],
  "attribution": [
    {
      "source": "NVD",
      "url": "https://nvd.nist.gov",
      "notice": "This product uses data from the NVD API but is not endorsed or certified by the NVD."
    },
    {
      "source": "CISA KEV",
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog",
      "notice": "Known exploited vulnerabilities from the CISA KEV catalog."
    },
    {
      "source": "FIRST EPSS",
      "url": "https://www.first.org/epss",
      "notice": "Exploit prediction scores from FIRST EPSS."
    }
  ]
}