libssh2 — security advisory

{
  "id": "956fe0c835f025cee84acfaf87d289ceaaecf2e6064bfc90caccdab5a59333e4",
  "url": "https://osv.dev/vulnerability/ALPINE-CVE-2026-66035",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ALPINE-CVE-2026-66035",
    "summary": "libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.",
    "evidence": "osv:ALPINE-CVE-2026-66035",
    "products": [
      {
        "name": {
          "value": "libssh2",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.11.1-r3",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      },
      {
        "name": {
          "value": "libssh2",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.11.1-r3",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      },
      {
        "name": {
          "value": "libssh2",
          "evidence": "/affected/2/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.11.1-r4",
            "evidence": "/affected/2/ranges"
          }
        ],
        "affected_versions": []
      },
      {
        "name": {
          "value": "libssh2",
          "evidence": "/affected/3/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.11.1-r4",
            "evidence": "/affected/3/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "ALPINE-CVE-2026-66035",
      "aliases": [
        "ALPINE-CVE-2026-66035"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "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"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "1.11.1-r3"
                }
              ]
            }
          ],
          "package": {
            "name": "libssh2",
            "purl": "pkg:apk/alpine/libssh2?arch=source",
            "ecosystem": "Alpine:v3.21"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2026-66035.json"
          },
          "ecosystem_specific": {}
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "1.11.1-r3"
                }
              ]
            }
          ],
          "package": {
            "name": "libssh2",
            "purl": "pkg:apk/alpine/libssh2?arch=source",
            "ecosystem": "Alpine:v3.22"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2026-66035.json"
          },
          "ecosystem_specific": {}
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "1.11.1-r4"
                }
              ]
            }
          ],
          "package": {
            "name": "libssh2",
            "purl": "pkg:apk/alpine/libssh2?arch=source",
            "ecosystem": "Alpine:v3.23"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2026-66035.json"
          },
          "ecosystem_specific": {}
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "1.11.1-r4"
                }
              ]
            }
          ],
          "package": {
            "name": "libssh2",
            "purl": "pkg:apk/alpine/libssh2?arch=source",
            "ecosystem": "Alpine:v3.24"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2026-66035.json"
          },
          "ecosystem_specific": {}
        }
      ],
      "modified": "2026-10-21T08:30:02.573713663Z",
      "provider": "osv",
      "upstream": [
        "CVE-2026-66035"
      ],
      "references": [
        "https://security.alpinelinux.org/vuln/CVE-2026-66035"
      ]
    },
    "related_cves": [
      {
        "value": "CVE-2026-66035",
        "evidence": "/upstream"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 391832,
  "published_at": "2026-07-24T17:17:35.547+00:00"
}