ghsa-4mf2-f3wh-gvf2
Vulnerability from github
Published
2021-05-25 18:42
Modified
2021-05-21 21:37
Severity ?
5.4 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Summary
Subdomain checking of whitelisted domains could allow unintended redirects in oauth2-proxy
Details

Impact

What kind of vulnerability is it? Who is impacted? For users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect.

For example, if a whitelist domain was configured for .example.com, the intention is that subdomains of example.com are allowed. Instead, example.com and badexample.com could also match.

Patches

Has the problem been patched? What versions should users upgrade to? This is fixed in version 7.0.0 onwards.

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading? Disable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.

Original Issue Posted by @semoac:

Whitelist Domain feature is not working as expected because is not matching a dot to ensure the redirect is a subdomain.

Expected Behavior

If whitelist domain is set to .example.com , then hack.alienexample.com should be rejected as a valid redirect.

Current Behavior

The code is removing the dot from .example.com and only checking if the redirect string end with example.com

Possible Solution

Here https://github.com/oauth2-proxy/oauth2-proxy/blob/c377466411f2aee180a732187edb638f2f7e57fb/oauthproxy.go#L661

Include the dot when checking the string: strings.HasSuffix(redirectHostname, "." + domainHostname)

Steps to Reproduce (for bugs)

``` package main

import ( "fmt" "strings" )

func validOptionalPort(port string) bool { if port == "" || port == ":*" { return true } if port[0] != ':' { return false } for _, b := range port[1:] { if b < '0' || b > '9' { return false } } return true }

func splitHostPort(hostport string) (host, port string) { host = hostport

colon := strings.LastIndexByte(host, ':')
if colon != -1 && validOptionalPort(host[colon:]) {
    host, port = host[:colon], host[colon+1:]
}

if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") {
    host = host[1 : len(host)-1]
}

return

}

func main() { domain := ".example.com" domainHostname, _ := splitHostPort(strings.TrimLeft(domain, ".")) redirectHostname := "https://hack.alienexample.com" if (strings.HasPrefix(domain, ".") && strings.HasSuffix(redirectHostname, domainHostname)) { fmt.Println("This should not have happen.")} }

```

Users of github.com/oauth2-proxy/oauth2-proxy are advised to update to github.com/oauth2-proxy/oauth2-proxy/v7

Show details on source website

To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/oauth2-proxy/oauth2-proxy/v7"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/oauth2-proxy/oauth2-proxy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "3.2.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2021-21291"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-601"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2021-05-21T21:37:23Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "### Impact\n_What kind of vulnerability is it? Who is impacted?_\nFor users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect.\n\nFor example, if a whitelist domain was configured for `.example.com`, the intention is that subdomains of `example.com` are allowed.\nInstead, `example.com` and `badexample.com` could also match.\n\n### Patches\n_Has the problem been patched? What versions should users upgrade to?_\nThis is fixed in version 7.0.0 onwards.\n\n### Workarounds\n_Is there a way for users to fix or remediate the vulnerability without upgrading?_\nDisable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.\n\n# Original Issue Posted by @semoac:\n\nWhitelist Domain feature is not working as expected because is not matching a dot to ensure the redirect is a subdomain.\n\n## Expected Behavior\n\nIf whitelist domain is set to `.example.com` , then `hack.alienexample.com`  should be rejected as a valid redirect.\n\n## Current Behavior\n\nThe code is removing the `dot`  from `.example.com`  and  only checking if the redirect string end with `example.com`\n\n## Possible Solution\nHere\nhttps://github.com/oauth2-proxy/oauth2-proxy/blob/c377466411f2aee180a732187edb638f2f7e57fb/oauthproxy.go#L661\n\nInclude the dot when checking the string:\n```\nstrings.HasSuffix(redirectHostname, \".\" + domainHostname)\n```\n\n## Steps to Reproduce (for bugs)\n\n```\npackage main\n\nimport (\n\t\"fmt\"\n\t\"strings\"\n)\n\nfunc validOptionalPort(port string) bool {\n\tif port == \"\" || port == \":*\" {\n\t\treturn true\n\t}\n\tif port[0] != \u0027:\u0027 {\n\t\treturn false\n\t}\n\tfor _, b := range port[1:] {\n\t\tif b \u003c \u00270\u0027 || b \u003e \u00279\u0027 {\n\t\t\treturn false\n\t\t}\n\t}\n\treturn true\n}\n\nfunc splitHostPort(hostport string) (host, port string) {\n\thost = hostport\n\n\tcolon := strings.LastIndexByte(host, \u0027:\u0027)\n\tif colon != -1 \u0026\u0026 validOptionalPort(host[colon:]) {\n\t\thost, port = host[:colon], host[colon+1:]\n\t}\n\n\tif strings.HasPrefix(host, \"[\") \u0026\u0026 strings.HasSuffix(host, \"]\") {\n\t\thost = host[1 : len(host)-1]\n\t}\n\n\treturn\n}\n\nfunc main() {\n\tdomain := \".example.com\"\n\tdomainHostname, _ := splitHostPort(strings.TrimLeft(domain, \".\"))\n\tredirectHostname := \"https://hack.alienexample.com\"\n\tif (strings.HasPrefix(domain, \".\") \u0026\u0026 strings.HasSuffix(redirectHostname, domainHostname)) { fmt.Println(\"This should not have happen.\")}\n}\n\n```\n\nUsers of `github.com/oauth2-proxy/oauth2-proxy` are advised to update to `github.com/oauth2-proxy/oauth2-proxy/v7`",
  "id": "GHSA-4mf2-f3wh-gvf2",
  "modified": "2021-05-21T21:37:23Z",
  "published": "2021-05-25T18:42:20Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-4mf2-f3wh-gvf2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-21291"
    },
    {
      "type": "WEB",
      "url": "https://github.com/oauth2-proxy/oauth2-proxy/commit/780ae4f3c99b579cb2ea9845121caebb6192f725"
    },
    {
      "type": "WEB",
      "url": "https://github.com/oauth2-proxy/oauth2-proxy/releases/tag/v7.0.0"
    },
    {
      "type": "WEB",
      "url": "https://pkg.go.dev/github.com/oauth2-proxy/oauth2-proxy/v7"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Subdomain checking of whitelisted domains could allow unintended redirects in oauth2-proxy"
}


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