CVE-2015-8557 in Pygments
Summary
by MITRE
The FontManager._get_nix_font_path function in formatters/img.py in Pygments 1.2.2 through 2.0.2 allows remote attackers to execute arbitrary commands via shell metacharacters in a font name.
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Analysis
by VulDB Data Team • 07/02/2022
The vulnerability identified as CVE-2015-8557 represents a critical command injection flaw within the Pygments code highlighting library version 1.2.2 through 2.0.2. This issue exists within the FontManager._get_nix_font_path function located in the formatters/img.py module, where the application fails to properly sanitize user input before incorporating it into shell commands. The flaw arises from insufficient validation of font name parameters, allowing malicious actors to inject shell metacharacters that get executed by the underlying operating system.
The technical implementation of this vulnerability stems from improper input handling within the image formatter component of Pygments, which is commonly used for syntax highlighting in various web applications and development environments. When a user-supplied font name contains special shell characters such as semicolons, pipes, or backticks, these characters are not properly escaped or sanitized before being passed to shell execution functions. This creates an attack surface where remote adversaries can craft malicious font names that, when processed by the vulnerable function, result in arbitrary command execution on the target system. The vulnerability maps to CWE-78, which specifically addresses improper neutralization of special elements used in OS commands, and aligns with ATT&CK technique T1059.001 for execution through command and script interpreters.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with potential access to the underlying system where Pygments is deployed. This could enable attackers to escalate privileges, exfiltrate sensitive data, or establish persistent access through the compromised system. The vulnerability is particularly dangerous in web applications that use Pygments for rendering user-generated content, as it allows for remote code execution without requiring authentication or additional attack vectors. Attackers can leverage this flaw to execute arbitrary commands with the privileges of the user running the Pygments application, potentially leading to full system compromise. The vulnerability affects environments where Pygments is used to generate images from code snippets, particularly in online code editors, documentation systems, and web-based development tools that process user input through the image formatter functionality.
Mitigation strategies for CVE-2015-8557 should prioritize immediate patching of affected Pygments versions to 2.0.3 or later, where the input sanitization has been properly implemented. Organizations should also implement input validation measures at the application level, ensuring that all font name parameters are properly escaped or filtered before being processed by any shell commands. Network-level defenses such as web application firewalls can help detect and block malicious payloads attempting to exploit this vulnerability. Additionally, system administrators should consider implementing least privilege principles for Pygments execution, limiting the privileges of the user account running the application to minimize potential damage from successful exploitation. Regular security auditing of third-party libraries and dependencies should be conducted to identify similar vulnerabilities in other components of the application stack, as this type of command injection vulnerability is common across many software systems and represents a fundamental security weakness that requires careful attention to input validation and sanitization practices.