CVE-2025-36397: IBM Application Gateway XSS Vulnerability

CVE-2025-36397 Overview

CVE-2025-36397 is an HTML injection vulnerability affecting IBM Application Gateway versions 23.10 through 25.09. This security flaw allows remote attackers to inject malicious HTML code into the application, which when viewed by victims, executes within their web browser in the security context of the hosting site. HTML injection vulnerabilities like this one (CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page) can enable attackers to manipulate page content, potentially leading to phishing attacks, credential theft, or session hijacking.

Critical Impact

Attackers can inject malicious HTML that executes in victims' browsers, potentially enabling phishing, session hijacking, and content manipulation within the trusted IBM Application Gateway security context.

Affected Products

• IBM Application Gateway 23.10
• IBM Application Gateway versions through 25.09

Discovery Timeline

• 2026-01-20 - CVE CVE-2025-36397 published to NVD
• 2026-01-20 - Last updated in NVD database

Technical Details for CVE-2025-36397

Vulnerability Analysis

This HTML injection vulnerability stems from improper neutralization of script-related HTML tags in web pages processed by IBM Application Gateway. The vulnerability requires an authenticated attacker with low privileges to exploit, but also requires user interaction—meaning a victim must view the injected content for the attack to succeed.

The attack is network-accessible and has a changed scope, meaning the vulnerable component (IBM Application Gateway) and the impacted component (victim's browser) are different. This cross-boundary impact allows attackers to breach confidentiality and integrity at a limited level without affecting availability.

Root Cause

The root cause is classified under CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page. IBM Application Gateway fails to properly sanitize or encode user-supplied input before rendering it in web pages. This allows specially crafted HTML content to be injected and rendered as legitimate page elements, enabling attackers to modify page appearance, inject forms, or redirect users to malicious sites.

Attack Vector

The attack vector is network-based, requiring the attacker to inject malicious HTML content through the IBM Application Gateway interface. The exploitation chain typically follows these steps:

1. An authenticated attacker identifies an input field or parameter that is reflected in the application's output without proper sanitization
2. The attacker crafts malicious HTML content designed to deceive users or capture sensitive information
3. The injected content is stored or reflected by the application
4. When legitimate users access the affected page, the malicious HTML renders in their browser within the application's trusted context
5. Victims may unknowingly interact with the injected content, potentially disclosing credentials or sensitive data

Unlike cross-site scripting (XSS), HTML injection typically focuses on manipulating page structure and content rather than executing JavaScript, though the boundary between these vulnerability classes can be blurry.

Detection Methods for CVE-2025-36397

Indicators of Compromise

• Unusual HTML elements or forms appearing on IBM Application Gateway pages that were not part of the original application design
• User reports of unexpected page content, redirects, or prompts for credentials on application pages
• Web server logs showing suspicious input patterns containing HTML tags in query parameters or form submissions
• Anomalous authentication attempts following user interaction with potentially compromised pages

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block requests containing suspicious HTML tags in user input fields
• Deploy content security policy (CSP) headers to restrict inline content and reduce the impact of injected content
• Monitor application logs for input validation errors and rejected requests containing HTML markup
• Use browser-based detection tools to identify DOM modifications that indicate injected content

Monitoring Recommendations

• Enable detailed logging on IBM Application Gateway to capture all user input and output rendering
• Configure SIEM rules to alert on patterns associated with HTML injection attempts, such as <script>, <iframe>, <form>, or <img> tags in unexpected parameters
• Implement user behavior analytics to detect anomalous access patterns following potential exposure to injected content
• Regularly audit application pages for unauthorized content modifications

How to Mitigate CVE-2025-36397

Immediate Actions Required

• Review the IBM Security Advisory for official patch information and upgrade guidance
• Identify all IBM Application Gateway instances running versions 23.10 through 25.09 in your environment
• Implement input validation and output encoding as an interim measure if immediate patching is not possible
• Review application logs for evidence of exploitation attempts prior to patching

Patch Information

IBM has released a security advisory addressing this vulnerability. Organizations running affected versions of IBM Application Gateway should consult the IBM Security Advisory for detailed patching instructions, upgrade paths, and version-specific remediation guidance. Apply the latest security updates as soon as possible following your organization's change management procedures.

Workarounds

• Deploy a web application firewall (WAF) in front of IBM Application Gateway to filter requests containing malicious HTML content
• Implement strict Content Security Policy (CSP) headers to limit the impact of any successfully injected content
• Restrict access to the IBM Application Gateway interface to trusted networks and users until patches can be applied
• Enable additional authentication controls to reduce the attack surface for authenticated attackers