CVE-2026-69246: Guzzle Noncanonical Host Can Bypass Host-based Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-v5mv-p594-2x33",
  "modified" : "2026-08-03T21:07:26Z",
  "published" : "2026-08-03T21:07:26Z",
  "aliases" : [ "CVE-2026-69246" ],
  "summary" : "Guzzle: Noncanonical host can bypass host-based checks",
  "details" : "### Impact\n\nIn affected versions, Guzzle gives a transport the request URI as text and supplies the `Host` header separately. The cURL handlers set `CURLOPT_URL` to the URI exactly as written and push that `Host` into `CURLOPT_HTTPHEADER`; `StreamHandler` does the same through `fopen()`. libcurl then parses the authority itself, percent-decoding it and, on an IDN-capable build, applying IDNA mapping, and uses the result to resolve, connect, name the TLS peer and address a proxy `CONNECT`, while the supplied `Host` suppresses the aligned one it would have generated. In `http://127.0.0.%31/` the URI host is one `filter_var()` rejects as an IP literal, yet libcurl decodes it to `127.0.0.1` and reaches loopback with no DNS lookup while the server receives `Host: 127.0.0.%31`.\n\nAn attacker who influences a fetched URI can therefore reach a host the application's checks excluded and read whatever it exposes of the response. The same divergence moves Guzzle's own decisions onto a spelling the transport does not use: `no_proxy` selects proxy routing from the literal host, and `RedirectMiddleware` decides from it whether to strip `Authorization` and `Cookie`. The cookie middleware extracts `Set-Cookie` against the URI Guzzle produced, not the authority contacted, so for a raw divergent URI the cookie is stored under the URI host as written. Where Guzzle rewrote that URI but left a divergent `Host`, or where the caller supplied one, the cookie is stored under the canonical name and replayed by ordinary later requests to it. With a third-party `UriInterface`, a host of `blocked.example.com@127.0.0.1` reaches `127.0.0.1` through all three handlers and generates `Authorization: Basic` from userinfo the application never wrote.\n\nExploitation requires the application to build a request URI from untrusted input and to make a host decision before handing it to Guzzle. Applications that only fetch URIs they construct themselves are not affected, and an exact allowlist of canonical names ordinarily fails closed; the exposure is to denylists, private-range and IP-literal checks, and any check that treats an unresolvable name as safe. The raw Unicode class needs an IDNA transformation somewhere: either a libcurl built with IDN support or Guzzle's own `idn_conversion`, off by default on both branches, which rewrites the URI in `Client::buildUri()` before a handler sees it and leaves a prebuilt request's explicit `Host` as written, while a request the client builds derives that header from the rewritten URI and produces no divergence. Noncanonical numeric spellings such as `127.1`, `2130706433`, `0x7f000001` and `0177.0.0.1` remain accepted after the patch and reach whatever the transport reads them as, loopback or a routable public host, and the cURL and stream handlers can differ, so a check comparing a host against an address as text stays bypassable. Guzzle does not offer SSRF protection, and neither cache poisoning nor cross-tenant compromise was established.\n\n### Patches\n\nThis is a summary; the patches are the authority. The issue is fixed in `7.15.2` and `8.0.1`, which validate the request host in all three built-in handlers before any network I/O. A URI host is rejected for a byte outside `0x21` to `0x7E`, a percent escape, a URI authority delimiter, unbalanced brackets, or numeric-looking parts followed by a trailing dot. That last rule is deliberately conservative and also refuses out-of-range forms libcurl keeps as names, such as `256.0.0.1.`. An explicit `Host` header must be printable ASCII, and on `7.15.2` free of percent escapes. The client also regenerates a derived `Host` when it rewrites the request URI. Versions before `7.15.2` and version `8.0.0` are affected.\n\n### Workarounds\n\nIf you cannot upgrade, constrain the host yourself before handing a URI to Guzzle, and constrain any explicit `Host` header separately, on every redirect hop. The URI rule assumes `$uri` is a validated `GuzzleHttp\\Psr7\\Uri`, so re-parse a third-party `UriInterface` with `new Uri((string) $uri)` first.\n\n```php\n$host = $uri->getHost();\n\nif (\n    preg_match('/\\A[\\x21-\\x7E]*\\z/D', $host) !== 1\n    || strpbrk($host, '%@/?#\\\\') !== false\n    || substr($host, -1) === '.'\n) {\n    throw new RuntimeException('Refusing to fetch this URI host.');\n}\n\nif (\n    preg_match('/\\A[\\x21-\\x7E]*\\z/D', $hostHeader) !== 1\n    || strpos($hostHeader, '%') !== false\n) {\n    throw new RuntimeException('Refusing to send this Host header.');\n}\n```\n\nIt differs from the patch in both directions: it refuses `example.com.`, which the patch accepts, and it does not canonicalize `127.1` or `0x7f000001`. Reparsing the URI separates a valid port from the host and rejects malformed bracket forms, so the snippet checks the host component alone. `idn_conversion => true` is not an access control, since IDNA maps `１２７。０。０。１` onto `127.0.0.1` and direct handler use bypasses it, and `Uri::getHost()` is not an SSRF boundary: it is the host as written, not the host a transport connects to. Where the destination matters, resolve the host and check the addresses, and use a separate cookie jar for untrusted origins.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "guzzlehttp/guzzle"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.15.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "guzzlehttp/guzzle"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.0.0"
      }, {
        "fixed" : "8.0.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/guzzle/guzzle/security/advisories/GHSA-v5mv-p594-2x33"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/guzzle/guzzle/pull/3907"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/guzzle/guzzle/pull/3908"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/guzzle/guzzle/commit/3aeea0406aab88cbbd86531313d7cebf8ae149a4"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/guzzle/guzzle/commit/744101956d78b7c1384d0cbf379db13e859167bf"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/guzzle/guzzle"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/guzzle/guzzle/releases/tag/7.15.2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/guzzle/guzzle/releases/tag/8.0.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-180", "CWE-436", "CWE-918", "CWE-941" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-03T21:07:26Z",
    "nvd_published_at" : null
  }
}