PDF Signer Server Side Template Injection (SSTI) Scanner

PDF Signer is a software utility used primarily by businesses and individuals who need to digitally sign PDF documents. It is deployed across various professional environments to streamline document signing processes, ensuring document integrity and authenticity. Users appreciate PDF Signer for its ease of use in creating and managing electronic signatures. It integrates into existing workflows and document management systems. Companies favor it for reducing paper use and maintaining a digital audit trail. Its intuitive interface appeals to users of varied technical expertise.

The software version in question, PDF Signer 3.0, has a critical vulnerability due to a lack of proper input validation for template handling. This flaw can lead to a Server-Side Template Injection (SSTI), allowing attackers to exploit and execute arbitrary code on the server. It poses a significant risk, given its high CVSS score. SSTIs allow attackers to manipulate templates to execute unintended commands or access sensitive data. This kind of vulnerability often results from inadequate security controls in the handling of input data.

Technical details of this vulnerability include improper handling of CSRF tokens in cookies, allowing attackers to inject malicious payloads into web requests. Specifically, the vulnerability exploits the server’s parsing of template strings, combined with arbitrary command execution, using input like malicious cookie headers. By embedding code within the cookie parsing mechanism, a hacker may bypass security controls, executing code under the server's authority, exploiting root:.*:0:0: as a regex pattern. Effective exploitation involves crafting specific HTTP requests that override normal execution flow.

The potential effects of exploiting this vulnerability are severe. If successfully exploited, it grants attackers remote execution of commands on the server hosting PDF Signer. This could lead to unauthorized administrative access, data theft, or complete server compromise. An attacker could implement persistent backdoors for continuous access, tamper with data, or disrupt business operations. Additionally, such compromises could impact customer trust and result in significant financial liabilities. Therefore, timely remediation and raising awareness among stakeholders is crucial to mitigate the risk.