{
  "cveId": "CVE-2023-48230",
  "url": "https://patchblox.com/security/cve/CVE-2023-48230",
  "summary": "CVE-2023-48230 is fixed in capnproto on 1 platform, first by DEBIAN-CVE-2023-48230, released November 21, 2023. It is not reported as exploited. Patch Radar priority: Urgent.",
  "title": "capnproto: Cap\u0027n Proto is a data interchange format and capability-based RPC system",
  "description": "Cap\u0027n Proto is a data interchange format and capability-based RPC system. In versions 1.0 and 1.0.1, when using the KJ HTTP library with WebSocket compression enabled, a buffer underrun can be caused by a remote peer. The underrun always writes a constant value that is not attacker-controlled, likely resulting in a crash, enabling a remote denial-of-service attack. Most Cap\u0027n Proto and KJ users are unlikely to have this functionality enabled and so unlikely to be affected. Maintainers suspect only the Cloudflare Workers Runtime is affected.  If KJ HTTP is used with WebSocket compression enabled, a malicious peer may be able to cause a buffer underrun on a heap-allocated buffer. KJ HTTP is an optional library bundled with Cap\u0027n Proto, but is not directly used by Cap\u0027n Proto. WebSocket compression is disabled by default. It must be enabled via a setting passed to the KJ HTTP library via \u0060HttpClientSettings\u0060 or \u0060HttpServerSettings\u0060. The bytes written out-of-bounds are always a specific constant 4-byte string \u0060{ 0x00, 0x00, 0xFF, 0xFF }\u0060. Because this string is not controlled by the attacker, maintainers believe it is unlikely that remote code execution is possible. However, it cannot be ruled out. This functionality first appeared in Cap\u0027n Proto 1.0. Previous versions are not affected.  This issue is fixed in Cap\u0027n Proto 1.0.1.1.",
  "published": "2023-11-21T21:15:08Z",
  "severity": "critical",
  "cvss": 9.8,
  "cvssVector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
  "epss": 0.01888,
  "epssPercentile": 0.79683,
  "priority": "Urgent",
  "priorityTier": 2,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "capnproto",
      "release": "Debian 13.5 (trixie)",
      "fixedVersion": "1.0.1-3",
      "fix": "DEBIAN-CVE-2023-48230",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2023-48230",
      "released": "2023-11-21T21:15:08Z"
    },
    {
      "platform": "linux",
      "product": "capnproto",
      "release": "Debian 14",
      "fixedVersion": "1.0.1-3",
      "fix": "DEBIAN-CVE-2023-48230",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2023-48230",
      "released": "2023-11-21T21:15:08Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-08T19:12:23Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}