Attack Surface: Arbitrary Command Execution via Preprocessors/Plugins
Description: Attackers exploit vulnerabilities in preprocessors or plugins to execute arbitrary commands on the server hosting or building the mdbook site.
How mdbook Contributes: mdbook's support for preprocessors and plugins, which are external executables, creates this attack vector. This is a direct feature of mdbook.
Example: An attacker crafts a malicious preprocessor (or compromises a legitimate one) that, when invoked by mdbook build, executes a shell command to download and run malware. Or, a plugin configured in book.toml is pointed to a malicious executable.
Impact: Complete system compromise, data exfiltration, installation of backdoors, lateral movement within the network.
Risk Severity: Critical
Mitigation Strategies:
* Strict book.toml Validation: Use a schema validator to ensure only whitelisted preprocessors/plugins with known-safe configurations are allowed. Treat book.toml as untrusted input if it can be externally influenced.
* Trusted Sources Only: Only use preprocessors/plugins from reputable, well-maintained sources with a strong security track record. Avoid custom or obscure ones unless thoroughly audited.
* Sandboxing: Run preprocessors/plugins within a sandboxed environment (e.g., Docker container) with limited privileges and resource access. This isolates the impact of a compromise.
* Least Privilege: Run mdbook build with a user account that has the absolute minimum necessary permissions. Never run as root.
* Code Review (for custom preprocessors/plugins): If developing custom preprocessors/plugins, conduct rigorous code reviews and security testing.
* Input Validation (for preprocessors/plugins): If the preprocessor/plugin accepts input, rigorously validate and sanitize that input to prevent command injection or other vulnerabilities.
* Regular Updates: Keep mdbook and all preprocessors/plugins updated to their latest versions to patch known vulnerabilities.
Attack Surface: Denial of Service (DoS) via Preprocessors/Plugins
Description: Attackers leverage preprocessors or plugins to consume excessive system resources (CPU, memory, disk), rendering the mdbook build process or the entire server unresponsive.
How mdbook Contributes: mdbook's execution of external preprocessors/plugins opens the door to resource exhaustion attacks. This is a direct consequence of mdbook's design.
Example: A malicious preprocessor enters an infinite loop or allocates massive amounts of memory, causing the mdbook build process to crash or the server to become overloaded. A plugin might perform computationally expensive operations on every page, slowing down the build significantly.
Impact: Disruption of service, inability to update the mdbook site, potential server instability.
Risk Severity: High
Mitigation Strategies:
* Resource Limits: Enforce strict resource limits (CPU time, memory, disk I/O) on preprocessor/plugin execution using tools like ulimit (Linux) or container resource constraints.
* Timeouts: Implement timeouts for preprocessor/plugin execution to prevent indefinite hangs or excessive processing time.
* Input Validation (for preprocessors/plugins): If the preprocessor/plugin accepts input, validate and sanitize it to prevent triggering resource-intensive operations.
* Rate Limiting (if applicable): If a preprocessor/plugin is invoked repeatedly, consider rate limiting to prevent abuse.
* Sandboxing: As with command execution, sandboxing helps contain resource usage.
Attack Surface: Information Disclosure via Preprocessors/Plugins
Description: A malicious or compromised preprocessor/plugin leaks sensitive information from the build environment or the server.
How mdbook Contributes: mdbook executes these external programs, giving them potential access to the build context. This is a direct consequence of using preprocessors/plugins.
Example: A preprocessor reads environment variables containing API keys or database credentials and sends them to an attacker-controlled server. A plugin accesses files outside the intended mdbook directory and exfiltrates them.
Impact: Exposure of sensitive data (API keys, credentials, source code, configuration files), potentially leading to further compromise.
Risk Severity: High
Mitigation Strategies:
* Minimize Sensitive Data in Build Environment: Avoid storing sensitive information (like API keys or credentials) in environment variables or files accessible to the build process. Use secrets management solutions.
* Sandboxing: Sandboxing restricts the preprocessor/plugin's access to the host system, limiting the scope of potential information disclosure.
* Code Review (for custom preprocessors/plugins): Thoroughly review the code to ensure it doesn't access or transmit sensitive data.
* Least Privilege: Ensure the user running mdbook has minimal access to sensitive resources.