CVE-2020-11053

Open Redirect in OAuth2 Proxy

As users can provide a redirect address for the proxy to send the authenticated user to at the end of the authentication flow. This is expected to be the original URL that the user was trying to access.
This redirect URL is checked within the proxy and validated before redirecting the user to prevent malicious actors providing redirects to potentially harmful sites.

However, by crafting a redirect URL with HTML encoded whitespace characters (eg. %0a, %0b,%09,%0d) the validation could be bypassed and allow a redirect to any URL provided.

Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.

CVE-2020-11053 has a CVSS score of 7.1 (High). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.1.1); upgrading removes the vulnerable code path.

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@rootxharsh and @iamnoooob provided this patch as potential solution:

From 4b941f56eda310b5c4dc8080b7635a6bfabccad4 Mon Sep 17 00:00:00 2001
From: Harsh Jaiswal <[email protected]>
Date: Fri, 1 May 2020 20:38:31 +0530
Subject: [PATCH] Fixes redirect issue

---
 oauthproxy.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/oauthproxy.go b/oauthproxy.go
index 1e9bb7c..f8beb4d 100644
--- a/oauthproxy.go
+++ b/oauthproxy.go
@@ -577,8 +577,9 @@ func validOptionalPort(port string) bool {

 // IsValidRedirect checks whether the redirect URL is whitelisted
 func (p *OAuthProxy) IsValidRedirect(redirect string) bool {
+       matched, _ := regexp.MatchString(`^/\s+/|\\`, redirect)
        switch {
-       case strings.HasPrefix(redirect, "/") && !strings.HasPrefix(redirect, "//") && !strings.HasPrefix(redirect, "/\\"):
+       case strings.HasPrefix(redirect, "/") && !strings.HasPrefix(redirect, "//") && !matched:
                return true
        case strings.HasPrefix(redirect, "http://") || strings.HasPrefix(redirect, "https://"):
                redirectURL, err := url.Parse(redirect)
--
2.17.1

This issue was also reported to us separately by @mik317 several hours later

The fix was implemented in #xxx and released as version 5.1.1

1. What is CVE-2020-11053? CVE-2020-11053 is a high-severity open redirect vulnerability in github.com/oauth2-proxy/oauth2-proxy (go), affecting versions < 5.1.1. It is fixed in 5.1.1. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
2. How severe is CVE-2020-11053? CVE-2020-11053 has a CVSS score of 7.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/oauth2-proxy/oauth2-proxy are affected by CVE-2020-11053? github.com/oauth2-proxy/oauth2-proxy (go) versions < 5.1.1 is affected.
4. Is there a fix for CVE-2020-11053? Yes. CVE-2020-11053 is fixed in 5.1.1. Upgrade to this version or later.
5. Is CVE-2020-11053 exploitable, and should I be worried? Whether CVE-2020-11053 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2020-11053 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2020-11053? Upgrade github.com/oauth2-proxy/oauth2-proxy to 5.1.1 or later.

Other vulnerabilities in github.com/oauth2-proxy/oauth2-proxy