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Introduction:
Open redirect vulnerabilities, often underestimated, serve as a critical enabler for sophisticated phishing campaigns and security chain attacks. The recent discovery of CVE-2025-4123 in Grafana, a popular open-source analytics and monitoring platform, exemplifies how a seemingly minor flaw in a trusted application can be weaponized to lend credibility to malicious actors. This vulnerability allows attackers to manipulate a trusted Grafana instance into redirecting users to an arbitrary, potentially malicious domain, bypassing user vigilance and security warnings.
Learning Objectives:
- Understand the mechanics and exploitation of Open Redirect vulnerabilities, specifically CVE-2025-4123 in Grafana.
- Learn the practical steps to test for and identify this vulnerability during security assessments and bug bounty hunting.
- Implement effective mitigation strategies to secure Grafana instances against this and similar attack vectors.
You Should Know:
1. Deconstructing the Open Redirect Payload
The provided payload, /public/..%2F%5Cevil.com%2F%3F%2F..%2F.., is a classic example of path traversal combined with URL encoding to confuse the web server’s path normalization logic.
Step-by-Step Guide:
- Step 1: Target Identification. Identify a target running a Grafana instance. The login page is typically found at
https://<target>/login. - Step 2: Payload Construction. The payload works by exploiting how Grafana’s `public/` route processes the subsequent path.
– `/public/` is a legitimate endpoint.
– `..%2F` is a URL-encoded forward slash (../), attempting to traverse up one directory level.
– `%5Cevil.com%2F%3F` is the core of the attack. `%5C` represents a backslash (\), and `%2F` is a forward slash (/). The use of a backslash can sometimes confuse path normalization routines on Windows-influenced systems or specific middleware, allowing the injector’s domain (evil.com) to be processed as part of the redirect location. - The final `%2F..%2F..` attempts further traversal to complete the bypass.
- Step 3: Execution and Verification. Append the payload to the target’s base URL: `https://target.com/public/..%2F%5Cevil.com%2F%3F%2F..%2F..`. If the instance is vulnerable, the server will respond with a `302 Found
or `301 Moved Permanently` redirect, sending your browser tohttps://evil.com`. You can test this without a live domain using an intercepting proxy like Burp Suite or with command-line tools.
Linux/macOS (curl command):
curl -I -L "https://target.com/public/..%2F%5Cevil.com%2F%3F%2F..%2F.."
The `-I` flag fetches only the headers, and `-L` follows redirects. Observe the `Location` header in the response to confirm the redirect.
Windows (PowerShell):
iwr -Uri "https://target.com/public/..%2F%5Cevil.com%2F%3F%2F..%2F.." -Method Head -MaximumRedirection 0
This sends a HEAD request and stops after the first response, allowing you to inspect the `Location` header directly.
2. The Real-World Impact: Beyond a Simple Redirect
An open redirect is not just a theoretical flaw; it is a powerful tool for attackers.
Step-by-Step Guide to Exploitation:
- Step 1: Crafting a Credible Phishing Link. An attacker creates a malicious link that appears perfectly legitimate:
https://trusted-company.com/public/..%2F%5Cphisher.com%2Flogin%3F%2F..%2F..`. The user sees the trusted domain (trusted-company.com`) and is more likely to click. - Step 2: The Deceptive Redirect. Upon clicking, the user is seamlessly redirected to `https://phisher.com/login`, a flawless replica of the real Grafana login page or another corporate login portal.
- Step 3: Credential Harvesting. The user, believing they are on a trusted site, enters their credentials, which are then captured by the attacker. This attack is particularly effective when combined with spam emails or malicious advertisements.
- Integrating Open Redirect Testing into Your Reconnaissance Workflow
Proactive discovery of such vulnerabilities is key for security professionals.
Step-by-Step Guide:
- Step 1: Automated Discovery. Use tools like `httpx` or `katana` to collect live URLs from your target scope. Filter for Grafana instances by looking for common paths like
/login,/public, or specific Grafana headers. - Step 2: Automated Testing. Incorporate the CVE-2025-4123 payload into your scanning scripts. Using `nuclei` is highly effective.
Nuclei Template Snippet (CVE-2025-4123.yaml):
id: CVE-2025-4123
info:
name: Grafana - Open Redirect
author: your-name
severity: medium
description: Open redirect vulnerability in Grafana via path traversal in the public endpoint.
reference:
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-4123
requests:
- method: GET
path:
- "{{BaseURL}}/public/..%2F%5C{{interactsh-url}}%2F%3F%2F..%2F.."
redirects: false
matchers:
- type: word
part: header
words:
- "Location: https://{{interactsh-url}}"
Run the template: nuclei -u https://target.com -t CVE-2025-4123.yaml.
– Step 3: Manual Verification. Always manually verify positive results from automated tools to eliminate false positives and understand the specific application context.
4. Mitigation and Patching: Securing Your Grafana Deployment
The primary defense is to apply the official patch. The Grafana security team has addressed this vulnerability in subsequent releases.
Step-by-Step Guide:
- Step 1: Version Check. Determine your current Grafana version. You can often find this information at the bottom of the login page or by accessing the `/api/health` endpoint.
- Step 2: Apply Updates. Upgrade your Grafana instance to the latest stable version. Refer to the official Grafana documentation for upgrade procedures specific to your installation method (Docker, binary, package manager).
- Official Advisory: Always check the Grafana security announcements for the specific versions that contain the fix for CVE-2025-4123.
- Step 3: Input Validation and Allow-listing. As a general security principle, implement strict input validation on all user-supplied URLs used for redirects. Reject any redirect URL that does not point to an explicitly allow-listed set of trusted domains. Do not rely on blacklists or simple string matching, as these are easily bypassed.
5. Advanced Exploitation: Chaining with Other Vulnerabilities
An open redirect can be the first step in a more devastating attack chain.
Step-by-Step Guide:
- Step 1: Bypassing SSO Protections. In some Single Sign-On (SSO) flows like SAML or OAuth, the “redirect_uri” parameter is validated. A flaw in this validation, combined with an open redirect on a whitelisted domain, could allow an attacker to trick the SSO provider into redirecting authentication tokens to a server they control.
- Step 2: Exploiting Client-Side Vulnerabilities. A redirect to a malicious site can trigger automatic downloads or exploit known browser vulnerabilities (e.g., XSS on the target domain if the context is not properly isolated). This can lead to remote code execution on the client’s machine.
- Step 3: Aiding in Malware Distribution. The trusted link can be used to distribute malware, as users are more likely to approve the download when it appears to originate from a legitimate corporate domain.
What Undercode Say:
- The Illusion of Trust is the Attacker’s Greatest Weapon. CVE-2025-4123 is a potent reminder that an application’s domain name is a primary signal of trust for end-users. By subverting this signal, attackers can dismantle the user’s first line of defense with devastating efficiency.
- Low-Severity Does Not Mean Low Impact. While often classified as a medium or low-severity issue, open redirects are a classic example of a “force multiplier” vulnerability. Their true danger is unlocked when chained with social engineering, making them a critical finding in any security assessment focused on real-world attack scenarios.
Analysis:
The disclosure of CVE-2025-4123 highlights a persistent class of web vulnerabilities that many organizations still fail to prioritize. Its existence in a widely adopted tool like Grafana underscores the necessity of continuous security testing across the entire software stack, not just custom code. For bug bounty hunters, this serves as a template: focus on common application paths in popular software and understand how encoding techniques can be used to bypass security checks. For defenders, it reinforces the need for a robust patch management process and defense-in-depth principles, where input validation is rigorously applied at every endpoint. Treating open redirects with the seriousness they deserve is a key step in building a resilient security posture against evolving phishing and redirection-based attacks.
Prediction:
The success of simple yet effective exploits like CVE-2025-4123 will fuel the development of more advanced, AI-driven phishing kits that automatically harvest and weaponize such vulnerabilities from public disclosures and scans. We predict a rise in “context-aware” phishing campaigns where the initial redirect analyzes the victim’s environment (location, language, device) from the trusted domain’s context before serving a hyper-personalized, malicious payload. Furthermore, as cloud-native technologies proliferate, misconfigurations and vulnerabilities in foundational components like monitoring dashboards will become a primary attack vector for initial cloud environment footholds, making hardening these systems non-negotiable.
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IT/Security Reporter URL:
Reported By: Cywer Learning – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
