CVE-2025-58353: Promptcraft Forge Studio XSS Vulnerability

CVE-2025-58353 Overview

CVE-2025-58353 is a Cross-Site Scripting (XSS) vulnerability affecting Promptcraft Forge Studio, a toolkit designed for evaluating, optimizing, and maintaining LLM-powered applications. The vulnerability stems from an ineffective input sanitization mechanism that uses regex blacklists to filter potentially dangerous content. Due to flawed implementation of these regex patterns, attackers can craft payloads that bypass the sanitization and execute arbitrary JavaScript code in the context of a user's browser session.

Critical Impact

Attackers can bypass input sanitization controls to inject and execute malicious JavaScript payloads, potentially leading to session hijacking, credential theft, and unauthorized actions within LLM-powered applications.

Affected Products

• Promptcraft Forge Studio (all versions)

Discovery Timeline

• 2025-09-04 - CVE-2025-58353 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-58353

Vulnerability Analysis

This vulnerability exists in all versions of Promptcraft Forge Studio due to a fundamentally flawed approach to input sanitization. The package attempts to prevent XSS attacks by using regex-based blacklists to remove dangerous patterns such as javascript: from user input. However, the implementation applies each replacement only once and fails to account for overlapping character sequences that can reconstitute dangerous tokens after sanitization.

When multi-character tokens are targeted for removal, the single-pass replacement can inadvertently create new dangerous sequences. For example, a carefully crafted input containing overlapping instances of the blacklisted pattern may have one occurrence removed while leaving behind characters that combine to form a valid javascript: URI. The "sanitized" output can then be used in href or src attributes, or injected directly into the DOM, resulting in arbitrary script execution.

Root Cause

The root cause is improper input validation (CWE-20) through the use of inadequate regex-based sanitization. The package relies on single-pass regex replacements like replace(/javascript:/gi, '') which do not recursively process input until all dangerous patterns are eliminated. This approach is inherently vulnerable to bypass techniques that exploit overlapping or nested payloads that reassemble into executable code after the sanitization routine completes.

Attack Vector

An attacker can exploit this vulnerability by submitting specially crafted input containing overlapping or nested instances of the javascript: protocol string. When the regex replacement removes one occurrence, the remaining characters combine to form a valid javascript: URI that was not present in the original detection pass.

The attack is network-accessible and requires user interaction (such as clicking a malicious link or viewing attacker-controlled content). Due to the changed scope characteristic of this XSS vulnerability, the impact extends beyond the vulnerable component to affect other resources in the same origin context, enabling high-severity confidentiality breaches and limited integrity impacts.

The vulnerability mechanism involves crafted payloads that exploit single-pass regex replacement. For detailed technical information and proof-of-concept examples, refer to the GitHub Security Advisory.

Detection Methods for CVE-2025-58353

Indicators of Compromise

• Unusual URL parameters or form inputs containing variations of javascript: with overlapping characters or nested patterns
• DOM elements with href or src attributes containing reconstituted JavaScript URIs
• Browser console errors or network requests indicating unexpected script execution from user-controlled input fields
• Log entries showing input containing patterns like javajavascript:script: or similar bypass attempts

Detection Strategies

• Implement Content Security Policy (CSP) headers to detect and block inline script execution attempts
• Deploy Web Application Firewall (WAF) rules to identify XSS bypass patterns targeting single-pass sanitization
• Monitor application logs for inputs containing recursive or overlapping dangerous protocol strings
• Use browser-based XSS auditing tools during security testing to identify bypass scenarios

Monitoring Recommendations

• Enable detailed logging of all user input processed by the sanitization functions
• Configure alerting for CSP violation reports indicating blocked script execution attempts
• Implement runtime application self-protection (RASP) to detect DOM manipulation anomalies
• Review application logs for patterns indicative of XSS payload testing or exploitation attempts

How to Mitigate CVE-2025-58353

Immediate Actions Required

• Implement a Content Security Policy (CSP) that restricts inline scripts and javascript: URI execution
• Replace regex-based blacklist sanitization with recursive or whitelist-based approaches
• Use established sanitization libraries such as DOMPurify instead of custom regex patterns
• Apply output encoding appropriate to the context (HTML, attribute, JavaScript) when rendering user input
• Review and audit all user input handling paths in applications using Promptcraft Forge Studio

Patch Information

There is currently no official fix available for this vulnerability. Users should implement the workarounds described below until a patch is released. Monitor the GitHub Security Advisory for updates on remediation status.

Workarounds

• Deploy a Content Security Policy header with script-src 'self' to prevent inline JavaScript execution
• Replace the vulnerable regex sanitization with a recursive approach that continues processing until no dangerous patterns remain
• Use a well-tested sanitization library like DOMPurify for all user input that may be rendered in the DOM
• Implement server-side validation in addition to client-side sanitization as defense in depth
• Avoid using user-controlled input directly in href, src, or DOM injection contexts without proper encoding

# Example CSP header configuration for nginx
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none';" always;