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GHSA-qqxw-m5fj-f7gv

MediumCVSS 5.9 / 10
Published Dec 20, 2021·Last modified Mar 13, 2026
Affected Components(0)

No affected components available

Description

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.

Risk Scores
Base Score
5.9

The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker needs basic access or low-level privileges. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a low impact on the availability of the system.

Threat Intelligence
5.4

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
1.12%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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