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Attack Tree Analysis for alibaba/fastjson2

Objective: Compromise application using fastjson2 by exploiting vulnerabilities within fastjson2.

Attack Tree Visualization

Compromise Application via fastjson2 **[CRITICAL NODE]**
├───[OR]─ **[HIGH RISK]** Exploit Deserialization Vulnerabilities **[CRITICAL NODE]**
│   ├───[OR]─ **[HIGH RISK]** Remote Code Execution (RCE) via Deserialization **[CRITICAL NODE]**
│   │   ├───[AND]─ **[HIGH RISK]** Exploit Polymorphic Deserialization/`autoType` Feature **[CRITICAL NODE]**
│   │   │   ├───[OR]─ **[HIGH RISK]** Leverage Known Gadget Classes **[CRITICAL NODE]**
│   │   │   │   └─── Utilize publicly known exploit chains (e.g., using classes present in common Java libraries on the classpath) to achieve RCE when deserialized.
│   │   │   ├───[OR]─ Bypass `autoType` Blacklist/Whitelist (if enabled)
│   │   │   │   ├─── Find Bypass Techniques
│   │   │   │   │   ├─── Case Sensitivity Issues
│   │   │   │   │   │   └─── Exploit case sensitivity differences in class names if blacklist/whitelist is case-sensitive.
│   │   │   │   │   ├─── Whitespace/Control Characters
│   │   │   │   │   │   └─── Inject whitespace or control characters into class names to bypass string-based filters.
│   │   │   │   │   ├─── Encoding/Obfuscation
│   │   │   │   │   │   └─── Use encoding techniques (e.g., URL encoding, Unicode escapes) to obfuscate class names.
│   │   │   │   │   └─── Logic Flaws in Filtering
│   │   │   │   │       └─── Identify and exploit weaknesses in the blacklist/whitelist logic itself.
│   │   │   └───[AND]─ **[HIGH RISK]** Craft Malicious JSON Payload **[CRITICAL NODE]**
│   │   │       └─── Construct a JSON payload that, when deserialized by fastjson2 with `autoType` enabled, instantiates and executes malicious code.
├───[OR]─ **[HIGH RISK]** Exploit Configuration Misuse/Weaknesses **[CRITICAL NODE]**
│   ├───[OR]─ **[HIGH RISK]** `autoType` Enabled Unnecessarily **[CRITICAL NODE]**
│   │   └─── **[HIGH RISK]** Exploit `autoType` (as described in Deserialization RCE) **[CRITICAL NODE]**
│   │       └─── If `autoType` is enabled where user-controlled JSON is processed, exploit deserialization vulnerabilities.
│   └───[OR]─ **[HIGH RISK]** Developer Misuse Leading to Vulnerabilities **[CRITICAL NODE]**
│       ├─── **[HIGH RISK]** Blindly Deserializing User Input **[CRITICAL NODE]**
│       │   └─── Application directly deserializes user-provided JSON without proper validation or sanitization, making it vulnerable to deserialization attacks.

Attack Tree Path: 1. Compromise Application via fastjson2 [CRITICAL NODE]

  • Attack Vector: This is the root goal. An attacker aims to leverage vulnerabilities in fastjson2 to gain unauthorized access or control over the application.
  • Risk: Critical. Successful compromise can lead to data breaches, system downtime, reputational damage, and legal repercussions.

Attack Tree Path: 2. Exploit Deserialization Vulnerabilities [HIGH RISK, CRITICAL NODE]

  • Attack Vector: Exploiting weaknesses in fastjson2's deserialization process, particularly when handling type information.
  • Risk: High. Deserialization vulnerabilities can lead to Remote Code Execution (RCE), Denial of Service (DoS), and Information Disclosure.

Attack Tree Path: 3. Remote Code Execution (RCE) via Deserialization [HIGH RISK, CRITICAL NODE]

  • Attack Vector: Crafting malicious JSON payloads that, when deserialized by fastjson2, execute arbitrary code on the server. This is the most severe outcome of deserialization vulnerabilities.
  • Risk: Critical. RCE allows the attacker to gain complete control over the application server, potentially leading to data theft, malware installation, and further attacks on internal systems.

Attack Tree Path: 4. Exploit Polymorphic Deserialization/autoType Feature [HIGH RISK, CRITICAL NODE]

  • Attack Vector: Abusing fastjson2's autoType feature, which allows specifying class types within the JSON payload. If enabled and not properly controlled, attackers can force the deserialization of malicious classes.
  • Risk: Critical. autoType is a primary enabler for deserialization RCE attacks in fastjson2.

Attack Tree Path: 5. Leverage Known Gadget Classes [HIGH RISK, CRITICAL NODE]

  • Attack Vector: Utilizing publicly known "gadget classes" (vulnerable classes often found in common Java libraries) in malicious JSON payloads. These classes can be chained together to achieve RCE when deserialized.
  • Risk: Critical. Gadget chains simplify RCE exploitation as attackers can reuse existing exploit techniques and don't need to find new vulnerabilities in fastjson2 itself.

Attack Tree Path: 6. Craft Malicious JSON Payload [HIGH RISK, CRITICAL NODE]

  • Attack Vector: Constructing a JSON payload that includes the necessary directives (e.g., @type with a malicious class) and data to trigger the desired exploit (RCE in this high-risk path).
  • Risk: Critical. The malicious payload is the weapon used to exploit the deserialization vulnerability. Successful crafting of this payload is essential for RCE.

Attack Tree Path: 7. Exploit Configuration Misuse/Weaknesses [HIGH RISK, CRITICAL NODE]

  • Attack Vector: Taking advantage of insecure configurations or misconfigurations of fastjson2 in the application.
  • Risk: High. Misconfigurations, especially enabling autoType unnecessarily, significantly increase the attack surface and likelihood of successful exploitation.

Attack Tree Path: 8. autoType Enabled Unnecessarily [HIGH RISK, CRITICAL NODE]

  • Attack Vector: Identifying and exploiting scenarios where autoType is enabled in the application's fastjson2 configuration but is not actually required for legitimate functionality.
  • Risk: Critical. Unnecessary autoType enablement directly opens the door to deserialization RCE attacks.

Attack Tree Path: 9. Exploit autoType (as described in Deserialization RCE) [HIGH RISK, CRITICAL NODE]

  • Attack Vector: Once autoType is confirmed to be enabled and processing user-controlled JSON, attackers can proceed with the deserialization RCE attack techniques described earlier (gadget classes, payload crafting).
  • Risk: Critical. This is the direct exploitation of the misconfiguration, leading to RCE.

Attack Tree Path: 10. Developer Misuse Leading to Vulnerabilities [HIGH RISK, CRITICAL NODE]

  • Attack Vector: Exploiting coding errors or insecure practices by developers when using fastjson2.
  • Risk: High. Developer errors are a common source of vulnerabilities. Blindly deserializing user input is a prime example of such misuse.

Attack Tree Path: 11. Blindly Deserializing User Input [HIGH RISK, CRITICAL NODE]

  • Attack Vector: Directly deserializing JSON data received from users without any validation or sanitization. This allows attackers to inject malicious payloads directly into the deserialization process.
  • Risk: Critical. This is a severe coding flaw that makes the application highly vulnerable to deserialization attacks, especially RCE.