CVE-2026-114627 in Web::Simple
Summary
by MITRE • 11/04/2026
Web::Simple versions before 0.036 for Perl do not escape values interpolated into double-quoted strings in HTML::Tags output.
Under use HTML::Tags or use XML::Tags, a double-quoted string literal becomes a StringThing object that holds each interpolated value as a separate part. The escaping step passes such objects through, and stringify joins their interpolated parts as is. A value passed on its own, as in <p>, $value, </p>, is entity-escaped, but the same value in "Hello $value" is not.
An attacker who controls a value that an application interpolates into a double-quoted string can inject script into the generated page.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in Web::Simple versions prior to 0.036 represents a critical server-side cross-site scripting flaw rooted in improper input validation and output encoding mechanisms within the Perl web framework. This issue specifically affects applications that utilize the HTML::Tags or XML::Tags modules for generating markup content. The core technical deficiency lies in how the framework handles string interpolation when values are embedded directly into double-quoted strings during template rendering. In a secure implementation, any dynamic data inserted into an HTML context must be rigorously escaped to neutralize special characters that could be interpreted as executable code by a client-side browser. However, due to this oversight, user-supplied input is rendered without adequate sanitization when processed through specific string interpolation patterns, creating a direct pathway for malicious script injection.
The technical mechanism of the flaw involves the internal object structure used by Web::Simple during template processing. When an application uses HTML::Tags or XML::Tags, any double-quoted string literal containing interpolated variables is converted into a StringThing object. This object stores each component of the string as separate parts to facilitate efficient rendering. The vulnerability arises in the escaping phase where these objects are processed. While values passed individually, such as within tag attributes like <p>$value</p>, undergo proper entity-escaping procedures, values interpolated inside double-quoted strings like "Hello $value" bypass this security check entirely. The stringify method joins these interpolated parts without applying necessary HTML encoding transformations. Consequently, if an attacker controls the value of $value and injects malicious JavaScript code, that code is output directly into the HTTP response body as raw text rather than being escaped into safe character entities.
From a threat modeling perspective, this vulnerability allows for stored or reflected cross-site scripting attacks depending on how the vulnerable variable is sourced. If the interpolated value originates from user input such as query parameters, form submissions, or cookies, an attacker can craft a payload that executes arbitrary JavaScript in the context of the victim's browser session when they view the affected page. This execution occurs within the trust boundary of the web application domain, enabling attackers to perform actions on behalf of the user, steal sensitive information like session tokens or credentials, deface the website, or redirect users to malicious sites. The impact is severe because it undermines the integrity and confidentiality guarantees provided by the same-origin policy, as the browser treats the injected script as legitimate code from the trusted domain hosting Web::Simple.
This flaw aligns with CWE-79, which classifies Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting. Specifically, it reflects a failure to apply output encoding in dynamic web content generation contexts where variable interpolation occurs within string literals rather than explicit tag attributes. In terms of the MITRE ATT&CK framework, this vulnerability facilitates techniques associated with Client-side Injection and potentially Credential Access if session hijacking is achieved through script execution. The lack of automatic escaping for interpolated strings represents a systemic design weakness in the template engine's security model, requiring developers to manually ensure safety rather than relying on built-in protections that are inconsistently applied across different string formatting methods within the framework.
To mitigate this vulnerability, organizations must upgrade Web::Simple to version 0.036 or later where the issue has been resolved by ensuring consistent escaping behavior for all interpolated values regardless of their context within double-quoted strings. For applications unable to immediately patch due to dependency constraints, a temporary workaround involves avoiding direct interpolation of untrusted user input into double-quoted string literals used in HTML::Tags or XML::Tags contexts. Instead, developers should construct tags using separate arguments where the escaping logic functions correctly, such as passing values explicitly rather than embedding them within interpolated strings. Additionally implementing Content Security Policy headers can provide a layer of defense-in-depth by restricting script execution sources, although this does not replace the need for fixing the underlying code flaw. Regular security audits and static analysis tools configured to detect improper output encoding patterns in Perl web applications are recommended to identify similar issues across the codebase before deployment.