CVE-2020-5233

OAuth2 Proxy before 5.0 has an open redirect vulnerability. Authentication tokens could be silently harvested by an attacker. This has been patched in version 5.0.

OAuth2 Proxy before 5.0 has an open redirect vulnerability. Authentication tokens could be silently harvested by an attacker. This has been patched in version 5.0.

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.

OAuth2 Proxy before 5.0 has an open redirect vulnerability. Authentication tokens could be silently harvested by an attacker. This has been patched in version 5.0.

OAuth2 Proxy before 5.0 has an open redirect vulnerability. Authentication tokens could be silently harvested by an attacker. This has been patched in version 5.0.

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.

OAuth2 Proxy before 5.0 has an open redirect vulnerability. Authentication tokens could be silently harvested by an attacker. This has been patched in version 5.0.