{"id":"CVE-2026-44889","aliases":["GHSA-fh3h-vg37-cc95","PYSEC-2026-251"],"title":"WebOb: Location header normalization during redirect leads to open redirect - again","summary":"WebOb: Location header normalization during redirect leads to open redirect - again","severity":"medium","cvss":6.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","vendor":"webob","product":"webob","ecosystem":"pip","affected":["webob < 1.8.10"],"patched":["webob 1.8.10"],"published":"2026-06-04","updated":"2026-09-10","sourceUpdated":"2026-09-10T03:50:49.442249208Z","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-fh3h-vg37-cc95","references":[{"url":"https://github.com/Pylons/webob/security/advisories/GHSA-fh3h-vg37-cc95"},{"url":"https://github.com/Pylons/webob/security/advisories/GHSA-mg3v-6m49-jhp3"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-44889"},{"url":"https://github.com/Pylons/webob/commit/1f681a4f17fc10777ef861e8b43ecb26053bc539"},{"url":"https://github.com/Pylons/webob/commit/2b9fbedafb31180c910cf8526e9ea72b4603d0bc"},{"url":"https://github.com/Pylons/webob"},{"url":"https://github.com/Pylons/webob/releases/tag/1.8.10"},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/webob/PYSEC-2026-251.yaml"}],"tags":["osv","pip"],"epss":0.0021,"epssPercentile":0.11528,"ingestedAt":"2026-07-18T19:01:59.080Z","slug":"CVE-2026-44889","body":"## Overview\n\n### 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\n\n## Affected packages\n\n- `webob < 1.8.10`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `webob 1.8.10`","depth":"sunlit","depthScore":34,"depthScoreParts":{"impact":33.6,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}