CVE-2026-17431 in PDF::WebKit
Summary
by MITRE • 08/13/2026
PDF::WebKit versions through 1.2 for Perl allow OS command injection via a 2-arg open() of the output path in to_pdf and of stylesheet paths in _style_tag_for.
to_pdf reads the generated PDF back from its path argument, and _style_tag_for reads each entry of the stylesheets list, by assigning the path to a local @ARGV and reading it with the diamond operator, which opens each @ARGV element with Perl's 2-arg open(). A value that begins or ends with a pipe ("| cmd", "cmd |") is run as a command rather than opened as a file, and one that begins with a redirect ("> path", ">> path") opens that path for write or append. to_file forwards its path argument to to_pdf and reaches the same read.
Any caller that forwards untrusted input as the output path or as a stylesheets entry can run a command under the process UID; with the "cmd |" form the command's output is returned in place of the PDF, and with the "> path" form the named file is truncated. Stylesheets may only be added to an HTML source, so a URL or file source exposes the output path alone.
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Analysis
by VulDB Data Team • 08/13/2026
This vulnerability exists within the PDF::WebKit Perl module version 1.2 and earlier, representing a critical command injection flaw that enables arbitrary code execution through improper input validation. The issue stems from how the module handles file paths in two primary functions: to_pdf and _style_tag_for. These functions utilize Perl's 2-arg open() function without adequate sanitization of user-supplied input, creating a pathway for malicious actors to execute system commands or manipulate files through carefully crafted input strings.
The technical exploitation occurs when untrusted input flows directly into the output path parameter of to_pdf or stylesheet paths in _style_tag_for. The vulnerability leverages Perl's diamond operator and 2-arg open() behavior where strings beginning or ending with pipe characters ("| cmd" or "cmd |") are interpreted as commands rather than file paths, while those starting with redirection operators ("> path" or ">> path") trigger file truncation or appending operations. This fundamental design flaw allows attackers to execute arbitrary shell commands with the privileges of the process running PDF::WebKit, typically a web server or application user.
The operational impact of this vulnerability extends beyond simple command execution, potentially enabling complete system compromise when PDF::WebKit is used in web applications or server-side processing contexts. Attackers can leverage this weakness to perform reconnaissance operations, establish persistent backdoors, exfiltrate data, or escalate privileges within the affected environment. The vulnerability affects any application that processes user-provided content through PDF::WebKit's PDF generation functions, particularly those accepting HTML input with external stylesheet references or direct file path parameters.
Security professionals should note this vulnerability maps directly to CWE-78 and CWE-94 within the Common Weakness Enumeration framework, representing both OS command injection and code injection vulnerabilities. From an ATT&CK perspective, this maps to T1059.001 (Command and Scripting Interpreter: PowerShell) and T1203 (Exploitation for Client Execution), with potential lateral movement capabilities through privilege escalation. The vulnerability demonstrates poor input validation practices and inadequate sanitization of user-provided data, making it particularly dangerous in web applications where input sources are often untrusted.
Mitigation strategies should include immediate patching of PDF::WebKit to version 1.3 or later, where the vulnerability has been addressed through proper input validation and sanitization. Organizations must also implement strict input filtering and validation for any user-supplied data that flows into PDF generation functions, particularly when handling external stylesheet references or file path parameters. Additional protective measures include running affected applications with minimal required privileges, implementing network segmentation, and monitoring for suspicious command execution patterns. Security teams should conduct comprehensive code reviews to identify similar vulnerabilities in other modules using Perl's 2-arg open() function or diamond operator without proper sanitization.
The root cause analysis reveals that this vulnerability results from a lack of secure coding practices and insufficient consideration of the implications of Perl's built-in file handling functions. Developers must understand that user input should never be directly passed to system-level operations without thorough validation and sanitization, particularly when dealing with file path manipulation or command execution contexts. This vulnerability underscores the critical importance of following secure coding guidelines and implementing proper input validation mechanisms in all software components that handle external data processing.
Organizations using PDF::WebKit in production environments must urgently assess their exposure to this vulnerability through comprehensive security audits and penetration testing exercises. The attack surface is particularly broad given that many web applications rely on PDF generation capabilities, making this an attractive target for automated exploitation tools. Regular security updates, proper access controls, and robust monitoring systems are essential defensive measures that should be implemented immediately to protect against potential exploitation of this critical vulnerability.