{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.5.0"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/osrg/gobgp/v4"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.6.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-49837"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-125"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-09T23:20:57Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n    GoBGP contains a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`.\n    A malformed BGP OPEN message can cause bytes from a following capability to be interpreted as part of the current capability. The most security-relevant case is the 4-octet AS capability, where a capability with `CapLen == 0` may cause the parser to read bytes from the following capability as the 4-octet AS value. This parsed value may later affect peer AS validation during BGP session establishment.\n\n### Details\nThe issue is in the BGP OPEN capability parser under:\n\n- `pkg/packet/bgp/bgp.go`\n- `pkg/packet/bgp/validate.go`\n- \nThe BGP OPEN optional parameter capability format includes a capability code, a capability length field, and a capability value. Each concrete capability decoder should only parse bytes inside the declared capability value boundary.\nIn affected versions, the generic capability parser records the declared `CapLen`, but several concrete capability decoders continue parsing from the full remaining capability buffer after advancing past the two-byte capability header. Conceptually, the vulnerable pattern is:\n```go\ndata = data[2:]\n// decoder reads from data without first limiting it to CapLen\n\n### PoC\nThe following parser-level proof of concept demonstrates the issue without requiring a full BGP session or a running `bgpd` instance.\nThe malformed capability uses:\n- Capability Code: `65` (`BGP_CAP_FOUR_OCTET_AS_NUMBER`)\n- Declared `CapLen`: `0`\n- Four following bytes: `00 00 fd e8`\n\nAlthough the capability declares an empty value, affected versions parse the following four bytes as the 4-octet AS value `65000`.\n\n### Impact\nA remote peer that can send a malformed BGP OPEN message to a GoBGP instance may cause capability values to be parsed from outside their declared `CapLen` boundaries.\nIn the 4-octet AS capability case, this may affect:\n- peer AS validation;\n- capability negotiation;\n- interpretation of malformed OPEN messages;\n- acceptance or rejection decisions during BGP session establishment.\nThis issue does not appear to be arbitrary memory corruption, remote code execution, or information disclosure. It is a protocol parser boundary validation issue that can affect BGP OPEN validation semantics.",
  "id": "GHSA-gjrg-jjr3-56cm",
  "modified": "2026-07-09T23:20:57Z",
  "published": "2026-07-09T23:20:57Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/osrg/gobgp/security/advisories/GHSA-gjrg-jjr3-56cm"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/osrg/gobgp"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "GoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries"
}