CVE-2021-32618: Flask Security Too Open Redirect Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6qmf-fj6m-686c",
  "modified" : "2024-09-20T21:06:55Z",
  "published" : "2021-05-17T20:51:27Z",
  "aliases" : [ "CVE-2021-32618" ],
  "summary" : "Open Redirect in Flask-Security-Too",
  "details" : "### Impact\nFlask-Security allows redirects after many successful views (e.g. /login) by honoring the ?next query param. There is code in FS to validate that the url specified in the next parameter is either relative OR has the same netloc (network location) as the requesting  URL.\n\nThis check utilizes Pythons urlsplit library. However many browsers are very lenient on the kind of URL they accept and 'fill in the blanks' when presented with a possibly incomplete URL. As a concrete example - setting http://login?next=\\\\\\github.com\nwill pass FS's relative URL check however many browsers will gladly convert this to http://github.com. Thus an attacker could send such a link to an unwitting user, using a legitimate site and have it redirect to whatever site they want.\n\nThis is considered a low severity due to the fact that if Werkzeug by default ALWAYS ensures that the Location header is absolute - thus making this attack vector mute. It is possible for application writers to modify this default behavior by setting the 'autocorrect_location_header=False` which would then open up their application to this attack.\n\n### Patches\nNo patches as this time\n\n### Workarounds\nIf using Werkzeug, make sure to use the default Location header setting. If you can't - then use@app.after_request and write your own validation of the Location header if it is set.\n\n### References\nNo.\n\n### For more information\nIf you have any questions or comments about this advisory follow: https://github.com/Flask-Middleware/flask-security/issues/486\n\nThanks to Claroty (2021-0141) and @snoopysecurity for providing details and proof of concept.\n",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "Flask-Security-Too"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-32618"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Flask-Middleware/flask-security/commit/e39bb04615050448c1b8ba4caa7dacc0edd3e405"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/Flask-Middleware/flask-security"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/flask-security-too/PYSEC-2021-123.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://web.archive.org/web/20210517211717/https://github.com/Flask-Middleware/flask-security/issues/486"
  }, {
    "type" : "WEB",
    "url" : "https://web.archive.org/web/20211207121851/https://github.com/Flask-Middleware/flask-security/security/advisories/GHSA-6qmf-fj6m-686c"
  }, {
    "type" : "WEB",
    "url" : "https://web.archive.org/web/20220410062740/https://github.com/Flask-Middleware/flask-security/pull/489"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-601" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-05-17T16:53:26Z",
    "nvd_published_at" : null
  }
}