threat-modeling.md

Threat Model Analysis for serde-rs/serde

Threat: Threat: Uncontrolled Deserialization of Arbitrary Data Leading to RCE via deserialize_any Misuse or Format-Specific Vulnerabilities

• Description: An attacker crafts malicious input data that exploits either:
  • deserialize_any Misuse: The application uses deserialize_any in a way that allows the attacker to influence the type being deserialized. If the attacker can trick the application into deserializing data as a type with a vulnerable Deserialize implementation (including custom implementations or those in third-party crates), this can lead to RCE. This is especially dangerous with non-self-describing formats.
  • Format-Specific Deserializer Vulnerabilities: The attacker exploits a known or zero-day vulnerability in the format-specific deserializer (e.g., a bug in serde_json, serde_yaml, or a less common format's deserializer). serde provides the framework, but the actual parsing is done by these crates. A vulnerability here, combined with attacker-controlled input, can lead to RCE.
• Impact:
  • Remote Code Execution (RCE): The attacker gains the ability to execute arbitrary code on the server, leading to complete system compromise.
• Serde Component Affected:
  • serde::de::Deserialize trait (and its implementations, especially those in third-party crates or custom implementations).
  • serde::de::Deserializer trait.
  • Format-specific deserializers (e.g., serde_json::from_str, serde_yaml::from_str, bincode::deserialize).
  • Functions that use deserialize_any incorrectly.
• Risk Severity: Critical.
• Mitigation Strategies:
  • Avoid deserialize_any with Untrusted Input: This is the most crucial mitigation for this specific threat. If you must use deserialize_any, ensure the resulting type is strictly validated and cannot be influenced by the attacker. Prefer strongly-typed deserialization whenever possible.
  • Use Safe Deserializers: Choose well-vetted and actively maintained format-specific deserializers. Keep them updated to the latest versions to benefit from security patches.
  • Strict Input Validation: Implement rigorous input validation before deserialization, even with seemingly safe deserializers. This acts as a defense-in-depth measure.
  • Fuzz Testing: Regularly fuzz test the deserialization logic, including the format-specific deserializers, with a wide range of malformed inputs.
  • Sandboxing: Consider running the deserialization process in a sandboxed environment to limit the impact of any potential RCE.
  • Vulnerability Scanning: Regularly scan your dependencies (including format-specific deserializers) for known vulnerabilities.

Threat: Threat: Vulnerabilities in Custom Deserialize Implementations Leading to RCE

• Description: A developer implements the Deserialize trait manually and introduces a vulnerability that allows an attacker to achieve remote code execution. This could involve unsafe code, buffer overflows, use-after-free errors, or other memory safety issues within the custom implementation. The attacker provides crafted input that triggers the vulnerability during deserialization.
• Impact:
  • Remote Code Execution (RCE): The attacker gains the ability to execute arbitrary code on the server.
• Serde Component Affected:
  • serde::de::Deserialize trait (specifically, the custom implementation).
  • serde::de::Deserializer trait.
• Risk Severity: Critical.
• Mitigation Strategies:
  • Avoid Unsafe Code: Minimize or eliminate the use of unsafe code within the custom Deserialize implementation. If unsafe is absolutely necessary, ensure it is thoroughly reviewed and justified.
  • Extensive Testing: Thoroughly test the custom Deserialize implementation, including fuzz testing and testing with a wide variety of malformed and edge-case inputs.
  • Code Reviews: Have multiple experienced developers carefully review the custom implementation for security flaws, paying close attention to memory safety and potential vulnerabilities.
  • Leverage serde Attributes: Use serde attributes (e.g., rename, default, skip, with) whenever possible to reduce the amount of custom code and rely on serde's built-in, well-tested logic.
  • Follow Rust Safety Practices: Adhere to Rust's memory safety principles and best practices for error handling. Use appropriate data structures and avoid manual memory management.
  • Consider Alternatives: If the custom deserialization logic is complex, explore alternative approaches, such as using a different serialization format or deriving Deserialize and using helper functions to transform the data after deserialization.

Threat: Threat: Accidental Serialization of Sensitive Data (Leading to Significant Exposure)

• Description: A struct or enum containing highly sensitive data (e.g., private keys, internal database credentials) is inadvertently marked with #[derive(Serialize)]. This data is then serialized and exposed, for example, by being included in an API response that is logged by an external monitoring service, or stored unencrypted in a database. The direct involvement of serde is the unintentional derivation of Serialize.
• Impact:
  • Information Disclosure: Highly sensitive data is leaked, potentially leading to severe consequences like system compromise or financial loss.
  • Credential Compromise: Attackers gain access to credentials that grant them extensive control over the system or other sensitive resources.
• Serde Component Affected:
  • serde::ser::Serialize trait (and its implementations, especially via #[derive(Serialize)]).
  • serde::ser::Serializer trait.
• Risk Severity: High.
• Mitigation Strategies:
  • Selective Derivation: Only derive Serialize on data structures that are explicitly intended to be serialized. Avoid deriving it "just in case."
  • Field-Level Control: Use #[serde(skip)] to explicitly prevent serialization of all sensitive fields, even if the struct itself is serializable. This is a crucial defense.
  • Custom Serialize Implementation: Implement the Serialize trait manually for fine-grained control. This allows you to redact, encrypt, or otherwise protect sensitive data before it is serialized.
  • Code Reviews: Thoroughly review all code changes that involve adding or modifying Serialize derivations, paying very close attention to the data being exposed.
  • Data Classification Policy: Implement and enforce a strict data classification policy to identify sensitive data and ensure it is handled appropriately during serialization.
  • #[serde(with = "...")] for Encryption: Use the with attribute to specify a custom serialization module that encrypts sensitive fields during serialization, providing an additional layer of protection.