# URL Redirection to Untrusted Site ('Open Redirect') (CWE-601)

A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect.

**Stack:** Go

- Prevalence: Medium 3 languages covered
- Impact: Medium Review recommended
- Prevention: Documented 4 fix examples

**OWASP:** Broken Access Control (A01:2021-Broken Access Control) - #1

## Description

An open redirect vulnerability occurs when an application takes user input and uses it to redirect the user to a different URL. Attackers can exploit this to redirect users to malicious sites.

## Prevention

Prevention strategies for Open Redirect based on 1 Shoulder detection rules.

### Go

Validate redirect URLs against an allowlist of trusted domains

## Warning Signs

- [MEDIUM] User input flows to redirect without validation

## Consequences

- Gain Privileges
- Bypass Protection Mechanism

## Mitigations

- Validate URLs against an allowlist of trusted domains
- Use a mapping system rather than direct URL parameters
- Display warning pages before redirecting to external sites

## Detection

- Total rules: 4
- Languages: go, javascript, typescript, python

## Rules by Language

### Go (1 rules)

- **Open Redirect** [MEDIUM]: User-controlled input used in http.Redirect without URL validation.
  - Remediation: Validate redirect URLs against a whitelist of allowed domains.

```go
allowed := map[string]bool{"example.com": true}
u, err := url.Parse(redirectURL)
if err != nil || !allowed[u.Host] {
    http.Error(w, "Invalid redirect", 400)
    return
}
http.Redirect(w, r, redirectURL, http.StatusFound)
```

Learn more: https://shoulder.dev/learn/go/cwe-601/open-redirect