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Mitigation Strategies Analysis for typst/typst

Mitigation Strategy: Strict Input Schema Validation for Typst Markup

  • Description:

    1. Define Allowed Typst Subset: Carefully analyze your application's needs and determine the minimum necessary set of Typst features, commands, and syntax required for its functionality. Document this as your "allowed Typst schema." This should be a subset of the full Typst language.
    2. Typst-Aware Schema Enforcement: Implement a validation step that understands Typst syntax, even if it's a simplified parser. This validator should analyze the user-provided Typst input and strictly check if it conforms exactly to your defined allowed schema. Avoid using generic input validation techniques that are not aware of Typst's structure.
    3. Reject Non-Conforming Typst Input: If the input contains any Typst commands, syntax, or features that are not part of your allowed schema, immediately reject the entire input. Provide a clear error message to the user indicating that the input is not valid according to the application's allowed Typst subset.

  • Threats Mitigated:

    • Malicious Command Injection via Typst (Low Severity): By restricting the allowed Typst commands, you directly reduce the attack surface related to potentially exploitable or unexpected behaviors from less common or complex Typst features.
    • Resource Exhaustion via Complex Typst Documents (Medium Severity): Limiting the allowed Typst features inherently restricts the complexity of documents users can submit, making it harder to create documents designed to exhaust rendering resources.
    • Exploitation of Unintended Typst Feature Interactions (Medium Severity): If certain combinations of Typst features, while individually safe, could lead to unexpected or exploitable behavior when combined, a strict schema can prevent users from crafting such inputs.

  • Impact:

    • Malicious Command Injection via Typst: Medium Reduction - Directly reduces the attack surface by limiting the available Typst commands.
    • Resource Exhaustion via Complex Typst Documents: Medium Reduction - Indirectly limits complexity by restricting features, but still possible to create resource-intensive documents within the allowed subset.
    • Exploitation of Unintended Typst Feature Interactions: High Reduction - Prevents the use of feature combinations outside the defined safe subset.

  • Currently Implemented:

    • Generally not implemented by default in projects using typst/typst. Applications typically process any valid Typst markup.

  • Missing Implementation:

    • Typst Input Processing Layer: Needs to be implemented as a dedicated layer before the input is passed to the core typst rendering engine. This requires developing a Typst-aware validator that understands your defined schema.

Mitigation Strategy: Resource Limits During Typst Rendering Process

  • Description:

    1. Identify Typst Rendering Resource Usage: Understand the typical resource consumption patterns of the typst rendering process (CPU, memory, time) for legitimate use cases in your application.
    2. Enforce Time Limits for Typst Compilation: Set a maximum allowed wall-clock time for the typst compilation and rendering process. If rendering takes longer than this limit, forcefully terminate the Typst process. This prevents runaway Typst processes from consuming resources indefinitely.
    3. Limit Memory Allocation for Typst Renderer: Restrict the maximum amount of memory that the typst rendering process is allowed to allocate. Use operating system-level mechanisms or process control libraries to enforce memory limits specifically on the Typst process.
    4. Control Output Size from Typst (if applicable): If your application generates output files (like PDFs) from Typst, monitor the size of the output file during rendering. If the output size exceeds a predefined limit, stop the Typst rendering process.

  • Threats Mitigated:

    • Denial of Service (DoS) via Typst Resource Exhaustion (High Severity): Prevents attackers from submitting specially crafted Typst documents that are designed to cause the typst rendering engine to consume excessive CPU time, memory, or generate extremely large output files, leading to a DoS.

  • Impact:

    • Denial of Service (DoS) via Typst Resource Exhaustion: High Reduction - Directly mitigates resource exhaustion DoS attacks by preventing Typst from consuming unlimited resources.

  • Currently Implemented:

    • Generally not implemented by default. Developers need to explicitly add resource limiting mechanisms around the execution of the typst rendering command or library calls.

  • Missing Implementation:

    • Typst Execution Environment: Needs to be implemented in the code that launches and manages the typst rendering process. This involves using process management tools or libraries to set resource limits specifically for the Typst process.

Mitigation Strategy: Sandboxing the Typst Rendering Environment

  • Description:

    1. Isolate Typst Process: Run the typst rendering process in a restricted and isolated environment. This can be achieved using:
      • Operating System Sandboxes: Utilize OS-level sandboxing features (like Linux namespaces, seccomp, or macOS sandbox profiles) to confine the typst process.
      • Containerization: Execute typst within a lightweight container (e.g., Docker, Podman). Containers provide process and resource isolation.
    2. Minimize Typst Process Privileges: Configure the sandbox or container to grant the typst rendering process the absolute minimum privileges necessary for its operation. Specifically:
      • Restrict System Calls: Limit the system calls available to the typst process to only those essential for rendering.
      • Network Isolation for Typst: Completely block or strictly control network access from within the sandboxed Typst environment, unless network access is absolutely required for your specific use case (which is unlikely for typical Typst rendering).
      • Limited File System Access for Typst: Restrict the file system access of the typst process. Ideally, provide a temporary, isolated file system with only the necessary input Typst document and a designated output directory. Prevent access to sensitive system files or application data.

  • Threats Mitigated:

    • Exploitation of Potential Typst Vulnerabilities (High Severity): If a security vulnerability is discovered within the typst library itself that could lead to code execution or system compromise, sandboxing significantly limits the potential damage. The compromised Typst process will be confined within the sandbox and unable to directly harm the host system or other application components.
    • Information Disclosure from Typst Process (Medium Severity): Sandboxing reduces the risk of a compromised Typst process being able to access and exfiltrate sensitive data from the system, as its file system and network access are restricted.

  • Impact:

    • Exploitation of Potential Typst Vulnerabilities: High Reduction - Significantly contains the impact of vulnerabilities within the Typst library itself.
    • Information Disclosure from Typst Process: Medium to High Reduction - Effectiveness depends on the strictness of the sandbox configuration and the sensitivity of data accessible within the sandboxed environment.

  • Currently Implemented:

    • Generally not implemented by default. Sandboxing requires a conscious effort to set up and configure the execution environment for typst.

  • Missing Implementation:

    • Deployment Environment Configuration: Needs to be implemented at the deployment infrastructure level. This involves choosing a suitable sandboxing technology and configuring it to properly isolate the typst rendering process during application execution.