URGENT: Patch Formbricks Now! CVE-2025-59934 Allows Unauthorized Password Resets

By CyberDudeBivash • September 28, 2025, 2:53 AM IST • URGENT SECURITY DIRECTIVE

This is a critical security alert for all developers and organizations using the popular open-source form-building tool, **Formbricks**. A high-severity vulnerability, assigned **CVE-2025-59934**, has been discovered in the password reset functionality. This flaw allows a remote, unauthenticated attacker to successfully reset the password of any user, including administrators, and gain complete control over your Formbricks instance. Given that Formbricks is often used to collect sensitive customer and user data, a full takeover of the application can lead to a significant data breach. The Formbricks development team has released a patch, and you must upgrade your instances immediately. This directive provides a technical breakdown of the flaw, a step-by-step remediation plan, and strategic advice for hardening your applications.

Disclosure: This is a technical security directive for developers and AppSec professionals. It contains affiliate links to best-in-class solutions for application security and incident response. Your support helps fund our independent research.

Application Security & Response Stack

A layered defense is crucial for protecting web applications and the servers they run on.

Web Application Firewall (Alibaba Cloud WAF): Your first line of defense. A WAF can provide a ‘virtual patch’ to block malicious Host headers and protect the password reset endpoint while you test and deploy the code update.
MFA Hardware (YubiKeys via AliExpress): The ultimate defense against account takeover. Even if an attacker resets a password, phishing-resistant MFA would block them from logging in.
Host Security (Kaspersky EDR): Detect what happens *after* a compromise. If an attacker takes over the app and tries to attack the underlying server, EDR is your essential tool for spotting them.
Secure Coding Training (Edureka): Prevent these flaws at the source. Invest in training your developers on the OWASP Top 10 and secure development practices.

Remediation Plan: Table of Contents

Chapter 1: The Threat – Dissecting the CVE-2025-59934 Password Reset Flaw

The password reset function is one of the most security-sensitive parts of any web application. It is the built-in mechanism for a user to prove their identity and regain access when a password is forgotten. A flaw here is a critical failure.

**CVE-2025-59934** is a **Host Header Injection** vulnerability within the Formbricks password reset workflow. The root cause is that the application incorrectly trusted the user-supplied HTTP `Host` header when constructing the password reset link.

How a Normal Password Reset Works

A user, Priya, goes to `https://forms.mycompany.com` and clicks “Forgot Password.”
She enters her email address, `priya@mycompany.com`.
The Formbricks application generates a unique, secret, single-use token.
The application then constructs a full URL, like `https://forms.mycompany.com/reset?token=SECRET_TOKEN`, and emails it to Priya.
Priya clicks the link, the application validates the secret token, and allows her to set a new password.

How the Vulnerability Breaks This Process

The flaw is in Step 4. The vulnerable version of Formbricks did not use a hardcoded, trusted domain name to build the reset link. Instead, it built the first part of the link (`https://forms.mycompany.com`) by looking at the `Host` header of the HTTP request that initiated the process.

An attacker can exploit this by sending a request to your server but with a modified `Host` header pointing to their own malicious domain.

Chapter 2: The Kill Chain – From Host Header to Full Account Takeover

The attack is simple, elegant, and devastatingly effective.

Step 1: The Request. The attacker goes to your Formbricks instance at `https://forms.mycompany.com`. They click “Forgot Password” and enter the email address of their target—for example, `admin@mycompany.com`. They intercept this request using a tool like Burp Suite.
Step 2: The Injection. The attacker modifies the intercepted HTTP request. They change the `Host` header from `forms.mycompany.com` to `attacker-evil-server.com`. They then send this modified request to your server.
Step 3: The Malicious Link. Your Formbricks application receives the request. It generates a valid, secret password reset token for the `admin@mycompany.com` user. However, when it builds the link to email to the admin, it uses the attacker’s `Host` header. It constructs the URL: `http://attacker-evil-server.com/reset?token=SECRET_TOKEN`.
Step 4: The Token Theft. Your server sends an email to the legitimate administrator. The email’s content, however, contains the attacker’s malicious link. If the admin is busy or not paying close attention, they might click it. The moment they click, their browser makes a request to `attacker-evil-server.com`, sending the valid `SECRET_TOKEN` directly to the attacker’s server logs.
Step 5: The Takeover. The attacker now has the valid reset token. They can now use this token on your legitimate site (`https://forms.mycompany.com/reset?token=SECRET_TOKEN`), complete the password reset process, set a new password for the administrator, and log in, gaining full control of your application and all its data.

Chapter 3: Your Immediate Remediation and Hunting Plan

You must act now to patch this vulnerability and check for signs of compromise.

Step 1 (Immediate): Patch Your Formbricks Instance

The only permanent fix is to update your application. The Formbricks developers have released a patched version that correctly uses a trusted, server-side configuration value to build the password reset link instead of the untrusted `Host` header.

Follow the official documentation for your deployment type (Docker, source, etc.) to upgrade to the latest secure version immediately.

Step 2 (Urgent): Hunt for Evidence of Compromise

You must assume you were targeted before you patched. Your SOC and admin teams need to hunt for these IoCs:

Analyze Web Server Logs: This is your most critical source of evidence. Search your NGINX, Apache, or other web server access logs for all `POST` requests to your password reset endpoint. Examine the `Host` header for every single one of these requests. If you find any request where the `Host` header does not match your legitimate domain name, you have found a confirmed exploitation attempt.# Example grep command for NGINX logs grep "POST /api/v1/users/password/reset" /var/log/nginx/access.log | grep -v "Host: forms.mycompany.com"
Audit Application Logs: Log in to the Formbricks admin UI. Go to the audit trail section. Look for all password reset events. Correlate the timestamps of these events with your web server logs. Look for any successful password changes for your administrator or other privileged accounts that seem suspicious or were not requested by the user.
Check for New Admin Accounts: While in the admin UI, check the user list for any new accounts, especially any with administrative privileges, that you do not recognize.

Step 3 (If You Cannot Patch): Implement a Virtual Patch

If you have a business-critical reason that you cannot apply the software update immediately, you must implement a temporary, compensating control with your Web Application Firewall (WAF).

Configure your WAF to inspect the `Host` header of all incoming requests. Create a rule that drops any request where the `Host` header does not exactly match your list of legitimate, trusted domain names. A cloud WAF from a provider like Alibaba Cloud can be used to deploy this rule quickly across your entire infrastructure.

Chapter 4: Strategic Hardening – A Defense-in-Depth Approach

This vulnerability is a classic example of a single point of failure. A mature security posture is about building layers of defense so that even if one control fails, another is there to stop the attack.

The Ultimate Defense: Phishing-Resistant MFA. This entire attack chain ends in an attacker trying to log in with a newly reset password. If your Formbricks administrator account was protected with strong Multi-Factor Authentication, the attack would have failed at the final step. The attacker would have the new password, but they would not be able to bypass the MFA prompt. Mandating strong, hardware-based MFA like YubiKeys for all administrative access is the single most effective strategic defense against account takeover.

Chapter 5: Extended FAQ for Developers and SysAdmins

Q: Is my application vulnerable if it’s behind a reverse proxy or load balancer?
A: Yes, and in fact, this configuration can sometimes make the attack easier. Many reverse proxy setups are configured to pass the original `Host` header from the user’s request through to the backend application. You must ensure that your reverse proxy (e.g., NGINX, HAProxy) is configured to either overwrite the `Host` header with the correct value or to validate it before passing it to the backend.

Q: We use Formbricks for internal-only forms. Are we still at risk?
A: The risk is lower, as an external, unauthenticated attacker cannot reach your server. However, you are still vulnerable to an attacker who has already gained a foothold on your internal network. This vulnerability could be used by them to escalate their privileges by taking over your internal Formbricks admin account. The patch should still be applied.

Q: What is the OWASP category for this type of vulnerability?
A: This vulnerability falls under **A01:2021 – Broken Access Control** in the OWASP Top 10, as it allows an attacker to bypass the mechanism that controls who is allowed to change a password. The root cause also relates to **A04:2021 – Insecure Design** and **A10:2021 – Server-Side Request Forgery (SSRF)**, as the server is being made to generate a request to a domain supplied by the attacker.

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