vulnerabilities-workflow-1.md

Combined Vulnerability List

The following section details a potential vulnerability identified within the provided code.

1. Unbounded Memory Consumption due to Uncontrolled String Interning

• Description: The intern package employs a sync.Pool to manage maps used for storing interned strings. The String and Bytes functions within this package add new strings to these maps if they are not already present. Crucially, there is no mechanism in place to limit the number of strings that can be interned. An external attacker can exploit this by repeatedly invoking the String or Bytes functions with unique, attacker-controlled strings. This action causes the maps within the sync.Pool to grow continuously, leading to excessive memory consumption on the server hosting the application.

• Impact: Uncontrolled memory consumption can severely degrade application performance and potentially affect other applications sharing the same server. In critical scenarios, this can lead to application crashes due to out-of-memory errors, and in extreme cases, system instability if the server exhausts its memory resources. While having characteristics of a denial-of-service, the primary impact is resource exhaustion, significantly impacting application availability and performance. This is classified as a high severity vulnerability due to its potential to cause significant resource depletion and service disruption.

• Vulnerability Rank: high

• Currently Implemented Mitigations: None. The current implementation of the intern package lacks any measures to restrict the number of interned strings or manage the memory usage of the intern pool.

• Missing Mitigations:

  • Implement a Limit on Interned Strings: Introduce a cap on the maximum number of strings that can be interned. Once this limit is reached, the system should either refuse to intern new strings or implement a replacement strategy.
  • Introduce an Eviction Mechanism: Implement an eviction strategy for less frequently used interned strings. This could be achieved by replacing the simple map in sync.Pool with a more sophisticated cache like an LRU (Least Recently Used) cache. An LRU cache would automatically remove the least recently accessed strings when the cache reaches its capacity, thus controlling memory usage.
  • Evaluate Alternative String Interning Strategies: Explore alternative string interning approaches that might offer better memory efficiency or built-in mechanisms for managing resource usage, such as using a fixed-size hash table with collision resolution or exploring external caching solutions if persistence is required.

• Preconditions:

  • Active Usage of Interning: The target application must be actively utilizing the intern package's String or Bytes functions for string interning within its operational logic.
  • Attacker-Controlled Strings: An attacker must have the ability to influence or control the strings that are being passed to the intern.String or intern.Bytes functions. This could be achieved through various means, such as:
    • User Input: Injecting unique strings through user-provided input fields in web forms, API parameters, or command-line arguments if these inputs are subsequently interned.
    • External Data Sources: Manipulating external data sources (databases, files, network feeds) that the application reads and interns strings from.
    • Indirect Influence: Exploiting other vulnerabilities in the application that allow the attacker to indirectly control the strings being processed and interned.

• Source Code Analysis:

  1. sync.Pool and Map Initialization: In the file /code/intern.go, a sync.Pool named pool is defined. Each element in this pool is initialized as a map[string]string. This sync.Pool is intended to reuse map instances for efficiency.
  2. String(s string) Function: The String(s string) function is responsible for interning strings. It starts by obtaining a map m from the pool using pool.Get().
  3. String Existence Check: The function then checks if the input string s already exists as a key in the map m. This check is performed to determine if the string has already been interned.
  4. String Interning (Adding to Map): If the string s is not found in the map m, the function proceeds to intern the string by adding it to the map using the line m[s] = s. This effectively stores the string in the map, and subsequent calls with the same string will retrieve this interned version.
  5. Returning Map to Pool: Finally, the function returns the map m back to the pool using pool.Put(m). This makes the map available for reuse by subsequent calls to String or Bytes, enhancing performance through map recycling.
  6. Bytes(b []byte) Function: The Bytes(b []byte) function operates in a similar fashion to String(s string). It first converts the input byte slice b into a string and then utilizes the same interning mechanism described above, effectively interning the string representation of the byte slice.
  7. Absence of Size Limits: Critically, the code within the intern package lacks any logic to impose restrictions on the size of the map m or the total number of maps managed by the sync.Pool. As a result, every unique string processed by String or Bytes will be added to these maps, leading to unbounded memory consumption as the application handles more distinct strings over time. The sync.Pool dynamically creates new maps as needed to handle concurrent requests, exacerbating the potential for excessive memory usage.

• Security Test Case:

  1. Deployment: Deploy a test application that utilizes the intern package to intern strings. A suitable example would be a simple web application that accepts user input via a text field and interns this input before processing it (e.g., logging, displaying, or using it in further computations).
  2. Attack Script Development: Create a script (e.g., in Python using the requests library) designed to send a high volume of HTTP requests to the deployed application. Each request should be carefully crafted to include a unique string in its payload. For instance, the script can generate a series of strings like "attack_string_00001", "attack_string_00002", "attack_string_00003", and so on, ensuring each string is distinct. The script should be configured to send these requests rapidly in a loop to simulate a sustained attack.
  3. Resource Monitoring Setup: Before initiating the attack, set up resource monitoring for the application server. Utilize operating system tools such as top, htop, ps, or system monitoring dashboards to track the memory usage of the application's process. Specifically, monitor the Resident Set Size (RSS) of the application process, as this reflects the actual physical memory being used.
  4. Attack Execution and Monitoring: Execute the attack script, sending a large number of requests with unique strings to the test application. Simultaneously, continuously monitor the memory usage of the application server as configured in the previous step.
  5. Vulnerability Verification: Observe and analyze the memory usage patterns of the application process during the attack. If the memory footprint (RSS) of the application steadily and continuously increases over time as the attack progresses, and if this increase appears to be unbounded (i.e., memory keeps growing without leveling off), this confirms the presence of the unbounded string interning vulnerability. Further validation can be obtained by observing if the application's performance degrades over time due to increasing memory pressure, or if the application eventually crashes due to encountering out-of-memory errors. Such behavior definitively proves the vulnerability and highlights its potential impact on application stability and availability.