Quick answer: Open Redirect is when a site redirects the user to another address based on a parameter in the URL and does not check that target enough. The attacker uses your trusted site's address and appends their own malicious site as the redirect target. The user clicks a domain they know and trust; but the site silently takes them to the attacker's page. This does not steal data on its own, but it makes phishing attacks far more convincing, because the link really starts with your domain. The root fix: decide the redirect target not from a free address supplied by the user, but from an allow list on the server.

Open Redirect looks low impact alone but carries great value in chained attacks. The hardest job for an attacker is to gain the victim's trust; open redirect abuses exactly that trust. This article explains how open redirect works, why it must be taken seriously and how to defend properly.

How Open Redirect works

Many sites redirect the user to an address after login, after logout or when an action completes. This target is often carried by a parameter in the address bar. Its legitimate purpose is to return the user to the page they came from. The problem is when the site blindly trusts this parameter and redirects to any external address.

The attacker does this: takes your trusted site's redirect link, writes their own site in the target parameter and shares this link in an email or message. The victim sees the familiar domain at the start of the link, trusts it, clicks and ends up on the attacker's page. The key point: the link really starts from your site, which makes it very convincing.

Why it must be taken seriously

Use What open redirect adds
Phishing A link starting with a trusted domain convinces the victim
Credential theft Redirecting to a fake login page looks legitimate
Token leakage Sensitive parameters can be carried in the redirect chain
Filter bypass Security products let the trusted domain through

Open redirect acts as a multiplier especially in phishing and social engineering scenarios. Also, if the redirect target carries a sensitive token in an authentication flow, the impact grows to information disclosure.

Proper defense

1. Decide the target with an allow list

This is the strongest defense. Instead of supplying the full address they want to go to, the user should supply an option or a short id defined on the server. The server resolves the real address from this allow list. So redirecting to an external address is never possible.

2. Accept only internal relative paths

If redirection is unavoidable, only relative paths within your own site should be allowed, and a full external address should never be accepted. It must be verified server side that the address really belongs to your domain.

3. Make address validation robust

Simple text checks are easily bypassed; the domain must be validated strictly against the root component of the resolved address. Half checks are the most common source of open redirect.

4. Warn the user on external links

If redirecting off site is truly necessary, showing the user an interstitial warning page reduces the deceptiveness of a silent redirect.

Open redirect scanning with KAOS

We scan for open redirect flaws at scale with KAOS, DSET's AI powered autonomous security scanning engine. With its multi agent architecture KAOS discovers endpoints carrying a redirect parameter, tries in a controlled way to make them redirect to an external address, and when it can show the browser is actually redirected to an external domain it verifies this; it reports only proven findings. So you see, without false positive noise, the endpoints where security products and half checks can be bypassed. KAOS works alongside the human expert and documents every finding with a working proof.

Frequently asked questions

Is open redirect dangerous on its own? It does not steal data directly but makes phishing and credential theft far more convincing. Its impact is large in chained attacks, so it must not be neglected.

Is filtering dangerous words in the target address enough? No. A blacklist approach is bypassed with encoding and format variations. The safe way is an allow list and internal relative paths.

Does it only happen on the login page? No. It can happen on login, logout, after payment and in any redirect flow. If the redirect target comes from the user, there is risk.

Why is it more critical in authentication flows? If the redirect target carries a token or code, redirecting to an external address can leak this sensitive value to the attacker.

Sources

To detect open redirect flaws in your application with a working proof from KAOS and our expert team, contact DSET. From our Ankara Hacettepe Teknokent laboratory we provide penetration testing and secure code review.