CVE-2026-73858 in Freeform Plugin
Summary
by MITRE • 09/23/2026
Solspace Freeform plugin for Craft CMS 5.x is a super flexible form-building tool. From 5.0.0 through 5.10.13, submitted values from public Freeform forms can be evaluated by the isolated Twig renderer when rendered into HTML attributes. An unauthenticated attacker can place Twig expressions in submitted field values, including value attributes, and receive evaluated PHP, operating-system, or Craft filesystem-path constants in the form response. The isolated context was not shown to expose Craft globals, environment variables, credentials, arbitrary files, or code execution, so the confirmed impact is limited server and environment information disclosure and possible rendering errors. This issue is fixed in version 5.10.14.
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Analysis
by VulDB Data Team • 09/23/2026
The Solspace Freeform plugin for Craft CMS serves as a robust form-building solution widely deployed across web applications to manage user input, contact forms, and data collection workflows. Versions ranging from 5.0.0 through 5.10.13 contain a critical security flaw related to the handling of submitted field values within HTML attributes. The vulnerability stems from an insufficient sanitization process when these values are rendered into HTML attribute contexts by the isolated Twig renderer. While Freeform employs an isolated context for rendering templates to mitigate broader risks, this specific implementation fails to properly escape or neutralize special characters in user-supplied data before it is embedded into attribute strings. This oversight allows an unauthenticated attacker to inject malicious payloads directly through public-facing form submissions without requiring any prior authentication credentials.
The technical nature of this flaw aligns with CWE-79, which classifies Cross-Site Scripting (XSS) vulnerabilities involving improper neutralization of input within web pages. However, in this specific instance, the impact extends beyond typical client-side script execution due to the server-side evaluation capabilities inherent in Twig templates when improperly configured or exploited via attribute injection. By placing carefully crafted Twig expressions into submitted field values, an attacker can trigger the rendering engine to evaluate these expressions as part of the HTML output generation process. This mechanism allows for the extraction of sensitive information such as PHP constants related to operating system paths, Craft CMS filesystem structures, and other server-side environment details that are typically hidden from end-users.
The operational impact of this vulnerability is primarily centered on information disclosure rather than direct remote code execution or full system compromise. Because the Twig renderer operates within an isolated context, it does not expose global variables, database credentials, or arbitrary file contents to the attacker. Consequently, confirmed impacts are limited to the leakage of server and environment metadata, which can aid attackers in further reconnaissance efforts. Additionally, malformed input may cause rendering errors that could disrupt service availability for legitimate users, leading to potential denial-of-service conditions through resource exhaustion or application instability during template processing.
This vulnerability is categorized under MITRE ATT&CK technique T1592, specifically relating to Gathering Victim Host Information, as it enables the enumeration of server environment details. It also relates to CWE-601, URL Redirection to Untrusted Site in a Redirect Header, if the rendered output influences subsequent navigation or API calls based on injected values, though the primary vector here is information leakage via template rendering flaws. The lack of proper input validation and encoding for HTML attribute contexts represents a significant deviation from secure coding practices recommended by OWASP for handling dynamic content insertion into web pages.
To mitigate this risk, organizations utilizing affected versions must immediately upgrade to version 5.10.14 or later, where the issue has been resolved through enhanced sanitization protocols. Until an update can be applied, administrators should implement strict input validation rules on all public-facing forms to reject any content containing Twig syntax markers such as double curly braces. Additionally, deploying a Web Application Firewall with specific rule sets designed to detect and block template injection attempts in form submissions can provide temporary protection against exploitation. Regular security audits focusing on how third-party plugins handle user-supplied data in sensitive contexts are essential for maintaining the integrity of CMS-based applications.