{
  "crds_version": "0.1",
  "kind": "base",
  "id": "crds:cve-2021-40438",
  "revision": 1,
  "title": "Apache httpd mod_proxy — Request Forgery via Crafted URI Path",
  "summary": "A crafted request path makes the Apache web server's proxy module forward the request to an origin server the caller picks, turning the front-end into a relay into networks the attacker cannot otherwise reach. Versions 2.4.48 and earlier are affected.",
  "source_type": "cve",
  "severity": "critical",
  "cvss": {
    "score": 9,
    "vector": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H",
    "version": "3.1"
  },
  "epss": 0.99999,
  "exploitation": {
    "known_exploited": true,
    "exploit_available": false,
    "attack_complexity": "high",
    "kev_added": "2021-12-01",
    "prerequisites": "An Apache server 2.4.48 or earlier that has the proxy module enabled, reachable over the network. No credentials needed."
  },
  "remediation": {
    "patch_available": true
  },
  "mitre_attack": [
    "T1190"
  ],
  "kill_chain": "initial_access",
  "recommended_action": "Upgrade Apache past 2.4.48 or install your distribution's patched build; then audit proxy rules and logs for requests forwarded to origins you never configured.",
  "confidence": "high",
  "provenance": [
    {
      "fields": [
        "title",
        "summary",
        "cvss",
        "severity",
        "exploitation.attack_complexity",
        "exploitation.prerequisites",
        "exploitation.exploit_available",
        "remediation.patch_available",
        "references"
      ],
      "source": "https://nvd.nist.gov/vuln/detail/CVE-2021-40438",
      "retrieved_at": "2026-08-07T07:53:55.549Z",
      "confidence": "high",
      "extractor": "claude-code"
    },
    {
      "fields": [
        "exploitation.known_exploited",
        "recommended_action"
      ],
      "source": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog",
      "retrieved_at": "2026-08-07T07:53:55.549Z",
      "confidence": "high",
      "extractor": "claude-code"
    },
    {
      "fields": [
        "epss"
      ],
      "source": "https://api.first.org/data/v1/epss?cve=CVE-2021-40438",
      "retrieved_at": "2026-08-07T07:53:55.549Z",
      "confidence": "high",
      "extractor": "claude-code"
    }
  ],
  "references": [
    {
      "type": "cve",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-40438",
      "label": "NVD record"
    },
    {
      "type": "vendor_advisory",
      "url": "https://httpd.apache.org/security/vulnerabilities_24.html",
      "label": "Apache httpd 2.4 vulnerabilities list"
    },
    {
      "type": "other",
      "url": "https://www.debian.org/security/2021/dsa-4982",
      "label": "Debian security advisory DSA-4982"
    },
    {
      "type": "cisa",
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-40438",
      "label": "CISA Known Exploited Vulnerabilities entry"
    }
  ],
  "published_at": "2021-09-16T15:15:07.633Z",
  "issued_at": "2026-08-07T07:53:55.549Z",
  "tags": [
    "apache",
    "httpd",
    "mod-proxy",
    "ssrf",
    "web-server",
    "kev",
    "ransomware"
  ]
}