GHSA-QQXW-M5FJ-F7GV

Vulnerability from github – Published: 2021-12-20 18:02 – Updated: 2021-05-24 21:20
VLAI?
Summary
The pattern '/\domain.com' is not disallowed when redirecting, allowing for open redirect
Details

Impact

An open redirect vulnerability has been found in oauth2_proxy. Anyone who uses oauth2_proxy may potentially be impacted.

For a context [detectify] have an in depth blog post about the potential impact of an open redirect. Particularly see the OAuth section.

tl;dr: People's authentication tokens could be silently harvested by an attacker. e.g: facebook.com/oauth.php?clientid=123&state=abc&redirect_url=https://yourdomain.com/red.php?url%3dhttps://attacker.com/

Patches

@sauyon found the issue, and has submitted a patch. 

diff --git a/oauthproxy.go b/oauthproxy.go
index 72ab580..f420df6 100644
--- a/oauthproxy.go
+++ b/oauthproxy.go
@@ -517,7 +517,7 @@ func (p *OAuthProxy) GetRedirect(req *http.Request) (redirect string, err error)
 // IsValidRedirect checks whether the redirect URL is whitelisted
 func (p *OAuthProxy) IsValidRedirect(redirect string) bool {
    switch {
-   case strings.HasPrefix(redirect, "/") && !strings.HasPrefix(redirect, "//"):
+   case strings.HasPrefix(redirect, "/") && !strings.HasPrefix(redirect, "//") && !strings.HasPrefix(redirect, "/\\"):
        return true
    case strings.HasPrefix(redirect, "http://") || strings.HasPrefix(redirect, "https://"):
        redirectURL, err := url.Parse(redirect)

This patch will be applied to the next release, which is scheduled for when this is publicly disclosed.

Workarounds

At this stage there is no work around.

Severity ?
5.9 (Medium)
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:H/A:L
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/oauth2-proxy/oauth2-proxy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2020-5233"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-601"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2021-05-24T21:20:17Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Impact\nAn open redirect vulnerability has been found in `oauth2_proxy`. Anyone who uses `oauth2_proxy` may potentially be impacted. \n\nFor a context [detectify] have an in depth blog post about the potential impact of an open redirect. Particularly see the OAuth section.\n\n**tl;dr**: People\u0027s authentication tokens could be silently harvested by an attacker. e.g:\n`facebook.com/oauth.php?clientid=123\u0026state=abc\u0026redirect_url=https://yourdomain.com/red.php?url%3dhttps://attacker.com/`\n\n### Patches\n\n@sauyon found the issue, and has submitted a patch. \n\n```\ndiff --git a/oauthproxy.go b/oauthproxy.go\nindex 72ab580..f420df6 100644\n--- a/oauthproxy.go\n+++ b/oauthproxy.go\n@@ -517,7 +517,7 @@ func (p *OAuthProxy) GetRedirect(req *http.Request) (redirect string, err error)\n // IsValidRedirect checks whether the redirect URL is whitelisted\n func (p *OAuthProxy) IsValidRedirect(redirect string) bool {\n \tswitch {\n-\tcase strings.HasPrefix(redirect, \"/\") \u0026\u0026 !strings.HasPrefix(redirect, \"//\"):\n+\tcase strings.HasPrefix(redirect, \"/\") \u0026\u0026 !strings.HasPrefix(redirect, \"//\") \u0026\u0026 !strings.HasPrefix(redirect, \"/\\\\\"):\n \t\treturn true\n \tcase strings.HasPrefix(redirect, \"http://\") || strings.HasPrefix(redirect, \"https://\"):\n \t\tredirectURL, err := url.Parse(redirect)\n```\n\nThis patch will be applied to the next release, which is scheduled for when this is publicly disclosed.\n\n### Workarounds\n\nAt this stage there is no work around.",
  "id": "GHSA-qqxw-m5fj-f7gv",
  "modified": "2021-05-24T21:20:17Z",
  "published": "2021-12-20T18:02:38Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-qqxw-m5fj-f7gv"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2020-5233"
    },
    {
      "type": "WEB",
      "url": "https://github.com/oauth2-proxy/oauth2_proxy/commit/a316f8a06f3c0ca2b5fc5fa18a91781b313607b2"
    },
    {
      "type": "WEB",
      "url": "https://blog.detectify.com/2019/05/16/the-real-impact-of-an-open-redirect"
    },
    {
      "type": "WEB",
      "url": "https://github.com/oauth2-proxy/oauth2_proxy/releases/tag/v5.0.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "The pattern \u0027/\\domain.com\u0027 is not disallowed when redirecting, allowing for open redirect"
}


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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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