Description

pypdftk through 0.5 contains an OS command injection vulnerability in fill_form(), dump_data_fields(), and pdftk_cmd_util() that builds shell commands from caller-supplied paths. Attackers controlling pdf_path or out_file can inject shell metacharacters interpreted by subprocess.Popen with shell=True to execute OS commands as the Python process.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.8",
  "pubDate": "2026-10-14T15:17:16.710Z",
  "pubdate": "2026-10-14T15:17:16.710Z",
  "executiveSummary": "The pypdftk library, specifically through version 0.5, is susceptible to an OS command injection vulnerability. This vulnerability exists within the application's command construction logic where user-supplied file paths are improperly handled before being passed to the underlying system shell.\nBy manipulating parameters such as pdf_path or out_file, a remote or local attacker can inject arbitrary shell metacharacters. When processed by the library's internal functions, these metacharacters are interpreted by the operating system, leading to the execution of unintended commands with the privileges of the Python process.\nThis represents a critical security flaw as it allows for unauthorized remote code execution (RCE). The impact is severe, potentially leading to full system compromise, data exfiltration, or denial of service, depending on the permissions of the user running the application. Exploitation does not require authentication, provided the attacker can influence the input strings passed to the vulnerable functions.",
  "technicalDetails": "The vulnerability originates in the implementation of the fill_form(), dump_data_fields(), and pdftk_cmd_util() functions within the pypdftk library. These functions are designed to interface with the pdftk utility by constructing shell commands as strings. The root cause of this vulnerability is the use of the subprocess.Popen constructor with the shell=True argument while concatenating unvalidated user-supplied input directly into the command string.\nIn the vulnerable versions, the library accepts file path inputs for operations such as PDF form filling or data field dumping. Because these inputs are not sanitized to escape shell metacharacters (e.g., ;, |, &, $, `), an attacker can inject malicious shell commands. When the library executes the command via subprocess.Popen(cmd, shell=True), the Python interpreter passes the entire string to the system shell (e.g., /bin/sh or cmd.exe). The shell parses the metacharacters, effectively chaining the intended pdftk command with the attacker's injected command.\nThe attack flow follows a predictable pattern: 1) The attacker identifies an application using pypdftk that accepts user input for file operations. 2) The attacker crafts a malicious file path payload containing shell command separators. For example, providing an input such as 'input.pdf; rm -rf /;'. 3) The application passes this string to fill_form(). 4) The library constructs a command string that terminates the legitimate pdftk process prematurely and initiates the arbitrary command. 5) The system shell executes the injected command with the privileges of the host Python process. This vulnerability is present in pypdftk through version 0.5. There are no authentication requirements for exploitation, and the attack vector is direct, as it relies on the processing of inputs through the library's API functions. Post-exploitation impact typically involves arbitrary file system access, lateral movement, or the installation of persistent malicious payloads, as the attacker gains the execution context of the parent application."
}