CVE-2020-11053 is a medium-severity (CVSS 6.1) Open Redirect vulnerability in github.com/oauth2-proxy/oauth2-proxy. A fix is available for github.com/oauth2-proxy/oauth2-proxy — see the affected versions and patch details below.
Open Redirect in OAuth2 Proxy
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2020-11053.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-11053 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
github.com/oauth2-proxy/oauth2-proxyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
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 <[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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/oauth2-proxy/oauth2-proxy | all versions | 5.1.1go get github.com/oauth2-proxy/oauth2-proxy@v5.1.1 |
Affected Products
oauth2 proxyoauth2_proxy_projectDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/oauth2-proxy/oauth2-proxy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/oauth2-proxy/oauth2-proxy to 5.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-11053 is resolved across your whole dependency graph.
Workarounds
Stop reflecting attacker-controlled destinations: resolve every redirect target against an allowlist of paths or hosts you own, prefer a server-side key over a full URL in the request, and reject absolute URLs entirely where the flow only ever needs a relative one.
Frequently Asked Questions
Is CVE-2020-11053 in your dependencies?
Find it across Go, including transitive dependencies.