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attack-surface.md

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Attack Surface Analysis for firecracker-microvm/firecracker

Attack Surface: 1. Unauthenticated/Unauthorized API Access

  • Description: Lack of proper authentication or authorization controls on the Firecracker API socket allows unauthorized entities to interact with it.
  • Firecracker Contribution: Firecracker exposes a local socket API for controlling microVMs. If access to this socket is not restricted, it becomes an open door for malicious actions directly targeting Firecracker's control plane.
  • Example: A vulnerability in a host-level service allows an attacker to gain local access. The attacker then leverages this access to send commands to the Firecracker API socket, creating and controlling microVMs without any authorization checks by Firecracker itself.
  • Impact: Full control over microVM lifecycle, configuration manipulation, potential access to guest resources, denial of service, and host system compromise.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Restrict File System Permissions: Ensure the Firecracker API socket file has restrictive permissions, allowing only the intended user (e.g., the application managing Firecracker) to access it. This is the primary and most direct way to control access to the Firecracker API.
    • Principle of Least Privilege: Run the process interacting with the Firecracker API with minimal necessary privileges to limit the impact if that process is compromised.

Attack Surface: 2. API Parameter Injection and Manipulation

  • Description: Vulnerabilities in the Firecracker API's parameter parsing and validation logic allow attackers to inject malicious payloads or manipulate parameters in unexpected ways when interacting with Firecracker's API.
  • Firecracker Contribution: Firecracker's API relies on parsing and processing JSON payloads. Weaknesses in Firecracker's parsing or validation of these payloads are directly exploitable.
  • Example: An attacker crafts a malicious JSON payload for the PUT /machine/config API endpoint, injecting unexpected characters or values into fields like mem_size or vcpu_count. Due to insufficient input validation within Firecracker, this could lead to integer overflows, buffer overflows, or unexpected behavior in Firecracker's VMM.
  • Impact: MicroVM instability, crashes, resource exhaustion, potential privilege escalation within Firecracker, or even guest-to-host escape if vulnerabilities are severe in Firecracker's core logic.
  • Risk Severity: High
  • Mitigation Strategies:
    • Strict Input Validation (Firecracker Development): Developers using Firecracker rely on the Firecracker project to implement robust input validation and sanitization for all API parameters within Firecracker itself. Users should ensure they are using versions of Firecracker with known input validation issues addressed.
    • Fuzzing and Security Testing (Firecracker Project): The Firecracker project should regularly fuzz the Firecracker API with malformed and unexpected inputs to identify potential parsing vulnerabilities. Users benefit from these efforts by using patched versions.
    • Keep Firecracker Updated: Apply security patches and updates released by the Firecracker project to address known vulnerabilities in API handling. This is crucial for users to benefit from security improvements in Firecracker.

Attack Surface: 3. VMM Code Vulnerabilities

  • Description: Bugs in the Firecracker Virtual Machine Monitor (VMM) code, such as memory corruption issues, logic errors, or unhandled exceptions, can be exploited. These are vulnerabilities within Firecracker's core VMM.
  • Firecracker Contribution: Firecracker is the VMM. Vulnerabilities in its C codebase are direct attack surfaces.
  • Example: A vulnerability exists in the memory management within the Firecracker VMM when handling a specific sequence of guest instructions or virtio device interactions. A malicious guest can trigger this vulnerability, leading to a buffer overflow in the VMM, allowing code execution on the host via a Firecracker vulnerability.
  • Impact: Guest-to-host escape, full host system compromise, denial of service, information disclosure - all stemming from flaws in Firecracker's VMM.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Regular Security Audits and Code Reviews (Firecracker Project): The Firecracker project should conduct thorough security audits and code reviews of the VMM codebase to identify and fix potential vulnerabilities. Users benefit from these efforts through updated, more secure Firecracker releases.
    • Fuzzing and Static Analysis (Firecracker Project): The Firecracker project should employ fuzzing and static analysis tools to automatically detect potential bugs and vulnerabilities in the VMM code. Users benefit from these efforts through updated, more secure Firecracker releases.
    • Memory Safety Practices (Firecracker Development): The Firecracker development team should utilize memory-safe coding practices in the VMM development and leverage memory safety tools during development and testing. Users benefit from these practices through a more robust and secure Firecracker VMM.
    • Keep Firecracker Updated: Apply security patches and updates released by the Firecracker project promptly. This is the most direct action users can take to mitigate VMM vulnerabilities.

Attack Surface: 4. Virtual Device Emulation Vulnerabilities (Virtio Devices)

  • Description: Vulnerabilities in the emulation of virtual devices (especially virtio devices like network and block storage) within Firecracker can be exploited by a malicious guest. These are vulnerabilities within Firecracker's virtio device emulation.
  • Firecracker Contribution: Firecracker implements virtio device emulation. Bugs in Firecracker's virtio device emulation code are a direct attack vector.
  • Example: A vulnerability exists in the virtio-net device emulation within Firecracker. A malicious guest sends specially crafted network packets that exploit this vulnerability, causing a buffer overflow in the VMM and allowing guest-to-host escape due to a flaw in Firecracker's network device emulation.
  • Impact: Guest-to-host escape, denial of service, information disclosure, potential compromise of other microVMs on the same host - all originating from vulnerabilities in Firecracker's device emulation.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Secure Virtio Implementation (Firecracker Development): The Firecracker project must ensure the virtio device emulation code in Firecracker is robust and secure. Users rely on the Firecracker project for a secure implementation.
    • Virtio Feature Negotiation Control (Firecracker Configuration): Users can carefully control and limit the virtio features negotiated with the guest through Firecracker's configuration, to minimize the attack surface exposed through virtio devices.
    • Input Validation in Virtio Devices (Firecracker Development): The Firecracker project should implement strict input validation and sanitization for data received from the guest through virtio devices within the VMM code. Users benefit from this through a more secure Firecracker implementation.
    • Keep Firecracker Updated: Apply security patches and updates released by the Firecracker project, as virtio device vulnerabilities are often targeted. This is crucial for users to receive fixes for virtio emulation vulnerabilities.

Attack Surface: 5. Weak Jailer Configuration

  • Description: Misconfiguration of the Firecracker jailer, specifically insufficient restrictions in seccomp filters, namespaces, or cgroups, weakens the isolation of microVMs provided by Firecracker's jailer.
  • Firecracker Contribution: Firecracker includes and relies on a jailer for process isolation. Weak jailer configuration directly undermines Firecracker's security guarantees.
  • Example: The seccomp filters applied by Firecracker's jailer are too permissive, allowing a compromised guest process to make system calls that should be restricted. This allows the guest to escape the jail and gain broader access to the host system because Firecracker's jailer was not configured restrictively enough.
  • Impact: Guest-to-host escape, privilege escalation on the host, potential compromise of other microVMs and the host system - all due to insufficient isolation provided by Firecracker's jailer.
  • Risk Severity: High
  • Mitigation Strategies:
    • Strict Jailer Configuration: Users must use the most restrictive possible seccomp filters, namespaces, and cgroups for Firecracker's jailer. Follow Firecracker's security recommendations for jailer configuration precisely.
    • Principle of Least Privilege: Grant only the necessary capabilities and system calls to the jailed Firecracker process when configuring the jailer.
    • Regularly Review Jailer Configuration: Periodically review and audit the jailer configuration to ensure it remains secure and aligned with security best practices for Firecracker deployments.
    • Use Firecracker's Recommended Jailer: Utilize the jailer provided and recommended by the Firecracker project, as it is designed with security in mind. Deviating from recommended jailer practices increases risk.