CVE-2026-44889: WebOb Location Header Normalization During Redirect Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-fh3h-vg37-cc95",
  "modified" : "2026-07-18T17:27:38Z",
  "published" : "2026-06-04T14:33:35Z",
  "aliases" : [ "CVE-2026-44889" ],
  "summary" : "WebOb: Location header normalization during redirect leads to open redirect - again",
  "details" : "### Impact\n\nWhen WebOb normalizes the HTTP Location header to include the request hostname, it does so by parsing the URL that the user is to be redirected to with Python's `urllib.parse`, and joining it to the base URL. `urlsplit` (called internally by `urljoin`) however treats a `//` at the start of a string as a URI without a scheme, and then treats the next part as the hostname. `urljoin` will then use that hostname from the second part as the hostname replacing the original one from the request.\n\nIn a previous advisory https://github.com/Pylons/webob/security/advisories/GHSA-mg3v-6m49-jhp3 an attempt to fix this was made by forcing the replacement of `//` with `/%2f`, however this did not take into account that since Python 3.10 `urlsplit` internally strips ASCII tab, carriage return, and newline characters from the string, so `/\\t/attacker.com` gets turned into `//attacker.com` and the attacker is able to bypass the changes introduced in that previous advisory, thereby bringing back the problem that was attempted to be fixed.\n\n```\n>>> parse.urlparse(\"//attacker.com/some/path\")\nParseResult(scheme='', netloc='attacker.com', path='/some/path', params='', query='', fragment='')\n```\n\nWebOb uses `urljoin` to take the request URI and join the redirect location to it, so assuming the request URI is `https://example.org/` and the URL to redirect to is `/\\t/attacker.com/some/path/`:\n\n```\n>>> parse.urljoin(\"https://example.org/\", \"/\\t/attacker.com/some/path/\")\n'https://attacker.com/some/path/'\n```\n\nWhich redirects from `example.org` where we want the user to stay to `attacker.com`.\n\n### Patches\n\nThis issue has been fixed in WebOb 1.8.10.\n\n### Workarounds\n\nAny use of the `Response` class that includes a `location` can be rewritten to make sure to always pass a full URI that includes the hostname to redirect the user to, or to validate that the redirect target starts with a scheme (e.g. `http://` or `https://`) before assigning to `Response.location`.\n\n### References\n\n- https://github.com/Pylons/webob/security/advisories/GHSA-mg3v-6m49-jhp3\n- CVE-2024-42353\n\n### Thanks\n\n- Caleb Brown of Google",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "webob"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.8.10"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.8.9"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/Pylons/webob/security/advisories/GHSA-fh3h-vg37-cc95"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Pylons/webob/security/advisories/GHSA-mg3v-6m49-jhp3"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44889"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Pylons/webob/commit/1f681a4f17fc10777ef861e8b43ecb26053bc539"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Pylons/webob/commit/2b9fbedafb31180c910cf8526e9ea72b4603d0bc"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/Pylons/webob"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Pylons/webob/releases/tag/1.8.10"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/webob/PYSEC-2026-251.yaml"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-601" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-04T14:33:35Z",
    "nvd_published_at" : "2026-06-22T22:16:46Z"
  }
}