{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "koa",
          "vendor": "koajs",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 3.0.0, \u003c 3.1.2"
            },
            {
              "status": "affected",
              "version": "\u003c 2.16.4"
            }
          ]
        }
      ],
      "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "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"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-20",
              "description": "CWE-20: Improper Input Validation",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-02-26T01:45:45.668Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm"
        },
        {
          "name": "https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df"
        },
        {
          "name": "https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb"
        }
      ],
      "source": {
        "advisory": "GHSA-7gcc-r8m5-44qm",
        "discovery": "UNKNOWN"
      },
      "title": "Koa has Host Header Injection via `ctx.hostname`"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-27959",
    "datePublished": "2026-02-26T01:45:45.668Z",
    "dateReserved": "2026-02-25T03:24:57.792Z",
    "dateUpdated": "2026-02-26T01:45:45.668Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-27959\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-02-26T02:16:23.317\",\"lastModified\":\"2026-02-26T02:16:23.317\",\"vulnStatus\":\"Received\",\"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.\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N\",\"baseScore\":7.5,\"baseSeverity\":\"HIGH\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":3.9,\"impactScore\":3.6}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-20\"}]}],\"references\":[{\"url\":\"https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm\",\"source\":\"security-advisories@github.com\"}]}}"
  }
}