EUVD-2026-40323

fkie_cve-2020-11053

In OAuth2 Proxy before 5.1.1, there is an open redirect vulnerability. 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 the validation could be bypassed and allow a redirect to any URL provided. This has been patched in 5.1.1.

GHSA-j7px-6hwj-hpjg — Open Redirect in OAuth2 Proxy

Affected: Go: github.com/oauth2-proxy/oauth2-proxy

### Impact 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.

### Patches @rootxharsh and @iamnoooob provided this patch as potential solution: ``` From 4b941f56eda310b5c4dc8080b7635a6bfabccad4 Mon Sep 17 00:00:00 2001 From: Harsh Jaiswal <harsh@pop-os.localdomain> 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(…

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