Ecosyste.ms: Advisories

Security Advisories: MDE2OlNlY3VyaXR5QWR2aXNvcnlHSFNBLXFxeHctbTVmai1mN2d2

The pattern '/\domain.com' is not disallowed when redirecting, allowing for open redirect

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.

Permalink: https://github.com/advisories/GHSA-qqxw-m5fj-f7gv
JSON: https://advisories.ecosyste.ms/api/v1/advisories/MDE2OlNlY3VyaXR5QWR2aXNvcnlHSFNBLXFxeHctbTVmai1mN2d2
Source: GitHub Advisory Database
Origin: Unspecified
Severity: Moderate
Classification: General
Published: over 2 years ago
Updated: over 1 year ago

CVSS Score: 5.9
CVSS vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:H/A:L

Identifiers: GHSA-qqxw-m5fj-f7gv, CVE-2020-5233
References:

• https://nvd.nist.gov/vuln/detail/CVE-2020-5233
• https://blog.detectify.com/2019/05/16/the-real-impact-of-an-open-redirect/
• https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-qqxw-m5fj-f7gv
• https://github.com/oauth2-proxy/oauth2_proxy/commit/a316f8a06f3c0ca2b5fc5fa18a91781b313607b2
• https://github.com/oauth2-proxy/oauth2_proxy/releases/tag/v5.0.0
• https://github.com/advisories/GHSA-qqxw-m5fj-f7gv

Repository: https://github.com/oauth2-proxy/oauth2-proxy
Blast Radius: 1.0

Affected Packages