attack-surface.md

Attack Surface Analysis for jordansissel/fpm

Attack Surface: Command Injection via Input Parameters

• Description: Attackers inject malicious shell commands by manipulating input parameters passed directly to the fpm command-line interface.
• How fpm contributes: fpm relies on command-line arguments for configuration, including package names, versions, and descriptions. If these arguments are constructed using unsanitized external or user-provided data, fpm directly passes them to the underlying shell, creating a command injection vulnerability.
• Example:
  • A script uses user input to define the package name: fpm -s dir -t deb -n "webapp-${USER_INPUT}" ...
  • If USER_INPUT is maliciously crafted as ; touch /tmp/pwned #, the command becomes fpm -s dir -t deb -n "webapp-"; touch /tmp/pwned # ....
  • This results in the execution of touch /tmp/pwned on the system running fpm.
• Impact: Full system compromise, arbitrary code execution, data loss, denial of service, unauthorized access to the build environment.
• Risk Severity: Critical
• Mitigation Strategies:
  • Strict Input Sanitization: Thoroughly sanitize and validate all input parameters used in fpm commands, especially those originating from user input or external sources. Use allow-lists and escape shell-sensitive characters.
  • Parameterization (where possible): Avoid dynamic command construction. Use fixed parameters or safer methods for passing dynamic values if feasible.
  • Secure Coding Practices: Implement secure coding practices in scripts that generate fpm commands to prevent command injection vulnerabilities.
  • Principle of Least Privilege: Run fpm processes with the minimum necessary privileges to limit the impact of successful exploitation.

Attack Surface: Path Traversal Vulnerabilities in Input File Handling

• Description: Attackers exploit path traversal sequences (e.g., ../) in file paths provided as input to fpm to access files or directories outside the intended scope of the package.
• How fpm contributes: fpm accepts file paths as input for source directories, files to include in packages, and for scripts. If fpm does not rigorously validate and sanitize these paths, it becomes vulnerable to path traversal attacks.
• Example:
  • Using fpm -s dir -t deb -C /app/webapp -f ../../../etc/shadow -n mypackage .
  • Intended to package files from /app/webapp, this command is manipulated to include /etc/shadow from the root directory using ../../../etc/shadow.
  • The attacker could then extract the Debian package and potentially access the sensitive /etc/shadow file.
• Impact: Information disclosure (sensitive files included in the package), unauthorized access to files on the build system, potential for package manipulation by including unintended files.
• Risk Severity: High
• Mitigation Strategies:
  • Robust Path Validation: Implement strict validation and sanitization of all input file paths provided to fpm. Use canonicalization to resolve symbolic links and remove . and .. components.
  • Chroot Environment: Run fpm within a chroot environment to restrict its file system access to a designated directory, limiting the scope of path traversal exploits.
  • Principle of Least Privilege: Ensure fpm processes operate with minimal file system permissions, reducing the potential damage from path traversal.
  • Input Whitelisting: Define a whitelist of allowed input paths and reject any paths that fall outside this whitelist.

Attack Surface: Unsafe Handling of External Processes and Commands (Scripts)

• Description: fpm executes external commands and scripts defined through options like --before-install, --after-install, and custom package scripts. If these commands or scripts are constructed unsafely, it can lead to command injection or exploitation of vulnerabilities in external tools executed by fpm.
• How fpm contributes: fpm's design includes features that allow execution of arbitrary shell commands during the package building and installation lifecycle. If the construction or content of these commands/scripts is not carefully managed, fpm facilitates the execution of malicious code.
• Example:
  • Using --before-install "echo 'Pre-install script for version: $PACKAGE_VERSION'" where $PACKAGE_VERSION is derived from an external, potentially attacker-influenced source.
  • If $PACKAGE_VERSION is set to '; malicious_command #, the executed command becomes echo 'Pre-install script for version: '; malicious_command #.
  • This allows execution of malicious_command with the privileges of the fpm process during package installation.
• Impact: System compromise, privilege escalation, arbitrary code execution during package installation or removal, data manipulation, denial of service.
• Risk Severity: High
• Mitigation Strategies:
  • Avoid Dynamic Command Construction in Scripts: Minimize or eliminate the dynamic construction of commands within fpm scripts, especially when using external or user-provided data.
  • Parameterization for Scripts: Pass dynamic data to scripts as arguments rather than embedding it directly into the script code to prevent injection.
  • Secure Scripting Practices: Ensure all scripts executed by fpm are written securely, following best practices to prevent command injection and other vulnerabilities.
  • Static Analysis of Scripts: Use static analysis tools to scan scripts for potential security vulnerabilities before using them with fpm.
  • Principle of Least Privilege for Scripts: Run scripts with the minimum necessary privileges to reduce the potential impact of vulnerabilities.

Attack Surface: Insecure Plugin Usage

• Description: Malicious or vulnerable fpm plugins can introduce significant security risks, potentially allowing arbitrary code execution or compromising the build environment.
• How fpm contributes: fpm's plugin architecture allows extending its functionality, but using untrusted or poorly vetted plugins directly expands the attack surface of fpm itself. fpm loads and executes plugin code, inheriting any vulnerabilities or malicious behavior present in the plugin.
• Example:
  • A malicious fpm plugin could be designed to exfiltrate sensitive data from the build environment, modify package contents to include backdoors, or execute arbitrary code on the build system during the packaging process.
  • A vulnerable plugin, even if not intentionally malicious, could contain security flaws that are exploitable, leading to compromise of the build system.
• Impact: System compromise, arbitrary code execution, data exfiltration, package manipulation (supply chain attacks), backdoors in generated packages.
• Risk Severity: High to Critical (depending on the plugin's capabilities and vulnerabilities)
• Mitigation Strategies:
  • Strict Plugin Vetting and Auditing: Thoroughly vet, audit, and review the source code and security of any fpm plugins before using them.
  • Trusted Plugin Sources: Only use plugins from highly trusted and reputable sources with a strong security track record.
  • Principle of Least Privilege for Plugins: If possible, run plugins with restricted permissions or within a sandboxed environment to limit their potential impact.
  • Plugin Sandboxing/Isolation: Investigate and utilize any sandboxing or isolation mechanisms offered by fpm or the plugin ecosystem to limit plugin capabilities.
  • Regular Plugin Updates and Security Monitoring: Keep plugins updated to the latest versions and monitor for security advisories related to fpm plugins.