17 Apr, 2023

Memcached Protocol

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Tests security measures and simulates attacks to identify weaknesses.

The Memcached protocol is a simple, lightweight, and distributed caching protocol used to accelerate dynamic web applications by caching data in memory. Memcached is an open-source, high-performance, key-value caching system that stores data in memory and provides fast access to frequently used data, reducing the need to fetch data from the underlying data source, such as a database or an API, repeatedly. 

The Memcached protocol is based on a client-server architecture, where clients (applications) communicate with Memcached servers to store and retrieve data in a distributed and scalable manner. The Memcached protocol uses a simple, text-based or binary format for communication between clients and servers, with commands and responses encoded in a specific format. The protocol is designed to be efficient and optimized for performance, making it suitable for high-speed caching scenarios in web applications. 

Memcached Common Ports 

TCP port 11211: The default TCP/IP port for Memcached is 11211. This is the most common port used for communication between clients (applications) and Memcached servers over the TCP/IP protocol. 

UDP port 11211: Memcached also supports communication over the User Datagram Protocol (UDP) in addition to TCP/IP. The default UDP port for Memcached is also 11211. 

Tools for using Memcached Protocol 

There are several tools available for using the Memcached protocol for interacting with Memcached servers. Some of the popular tools are: 

Memcached: The official command-line tool provided by the Memcached project, allowing you to interact with Memcached servers using the Memcached protocol. It provides a simple command-line interface for storing, retrieving, and deleting data in Memcached servers. 

Telnet: A widely used command-line tool for connecting to remote servers and interacting with them over a network. You can use Telnet to manually send Memcached protocol commands to a Memcached server, allowing you to store, retrieve, and delete data in the cache. 

PHP Memcached Client Libraries: There are several PHP Memcached client libraries available, such as php-memcached, php-memcache, and Memcached extension for PHP. These libraries provide APIs for interacting with Memcached servers in PHP applications. 

Python Memcached Client Libraries: There are several Python Memcached client libraries available, such as python-memcached, pylibmc, and python3-memcached. These libraries provide APIs for interacting with Memcached servers in Python applications. 

Memcached GUI Clients: There are also graphical user interface (GUI) clients available for Memcached that provide a visual interface for interacting with Memcached servers. Some popular Memcached GUI clients include Memcached Manager, phpMemcachedAdmin, and MemAdmin. These tools provide a visual way to interact with Memcached servers using a user-friendly interface. 

Memcachedb: Memcachedb is a storage engine based on Memcached that allows you to store data in a persistent manner, unlike the original Memcached which stores data in volatile memory. Memcachedb provides a simple command-line interface for storing, retrieving, and deleting data using the Memcached protocol. 

libmemcached: libmemcached is a C/C++ client library that provides APIs for interacting with Memcached servers. It can be used in C/C++ applications to communicate with Memcached servers using the Memcached protocol. 

Useful Information 

Memcached uses a simple text-based protocol that operates over TCP/IP or UDP. The protocol is designed to be lightweight and efficient, allowing for fast data retrieval and storage operations. 

Memcached is a distributed in-memory key-value store, where data is stored in the form of key-value pairs. Keys are typically strings that identify the data, and values can be any arbitrary binary data, such as strings, numbers, or serialized objects. 

The Memcached protocol supports basic CRUD (Create, Read, Update, Delete) operations for managing data in the cache. The main operations supported by the Memcached protocol are: 

• SET: Used to store a value with a given key in the cache. 

• GET: Used to retrieve the value associated with a given key from the cache. 

• DELETE: Used to remove a key-value pair from the cache. 

• ADD: Used to store a value with a given key in the cache only if the key does not already exist. 

• REPLACE: Used to update the value associated with a given key in the cache only if the key already exists. 

• INCREMENT/DECREMENT: Used to increment or decrement the numeric value associated with a given key in the cache. 

• APPEND/PREPEND: Used to append or prepend data to the value associated with a given key in the cache. 

Memcached is designed to be a distributed caching system, allowing multiple Memcached servers to work together as a single logical cache. Clients can send requests to any Memcached server in the cluster, and the server can respond with the requested data if it is available in its local cache or forward the request to other servers in the cluster to retrieve the data. 

In addition to the text-based protocol, Memcached also supports a binary protocol, which is a more compact and efficient way of sending and receiving data compared to the text-based protocol. The binary protocol is typically used for higher performance and reduced network overhead in production environments. 

Memcached supports a CAS(Compare-and-Swap) mechanism that allows clients to perform atomic updates to a key-value pair, ensuring that updates are applied only if the current value matches a specified value. This helps to prevent concurrent modifications from overwriting each other’s changes. 

Memcached allows you to set an expiration time for each key-value pair, after which the pair will be automatically removed from the cache. Memcached also supports an LRU (Least Recently Used) eviction policy, where if the cache reaches its capacity, the least recently used key-value pairs are evicted to make room for new data. 

Books on Memcached 

“Memcached Third Edition” by Gerardus Blokdyk: This book focuses on diagnosing Memcached projects, initiatives, organizations, businesses and processes using accepted diagnostic standards and practices. 

“Memcached A Complete Guide” by Gerardus Blokdyk: This book also focuses on diagnosing Memcached projects, initiatives, organizations, businesses and processes using accepted diagnostic standards and practices. 

“Caching using Memcached in Open-Source Searching” by Sarswati Kumar Pandey: This book describes the execution time improvement by using Memcached – a key/value caching solution.   

“Developing Web Applications with Apache, MySQL, memcached, and Perl” by Patrick Galbraith: The book addresses using cache to enhance and speed up Web application development. 


Memcached has some vulnerabilities and weaknesses that you should be aware of when using it in your applications. Here are some important points to consider: 

Lack of authentication and authorization: Memcached does not provide built-in authentication or authorization mechanisms. This means that by default, any client that can connect to a Memcached server can perform operations (such as reading, writing, or deleting data) without authentication or authorization. This can be a security risk if you need to protect sensitive data or restrict access to certain clients. 

Exposure to the network: Memcached is designed to be a distributed caching system and typically runs on a network. This means that Memcached servers may be exposed to the public network, increasing the risk of unauthorized access or attacks from malicious actors. It’s important to properly configure network security measures, such as firewalls and access control lists (ACLs), to protect Memcached servers from unauthorized access. 

Potential for data leakage: Since Memcached stores data in memory, data stored in Memcached is volatile and can be lost if the server is restarted or if the cache is evicted due to capacity constraints. Additionally, if a Memcached server is compromised, an attacker may be able to access and retrieve data from the cache. It’s important to carefully consider the types of data that are stored in Memcached and implement appropriate security measures, such as encryption or data masking, if needed. 

Denial of Service (DoS) attacks: Memcached can be vulnerable to Denial of Service (DoS) attacks, where an attacker can flood the server with requests, overwhelming its resources and causing it to become unresponsive. This can lead to degradation of performance or even complete service disruption. It’s important to implement rate limiting, throttling, or other defensive mechanisms to protect against DoS attacks. 

Misconfiguration: Misconfiguring Memcached servers can also pose security risks. For example, leaving Memcached servers with default settings or not properly securing the network or access to the servers can result in vulnerabilities. It’s important to follow best practices for configuring Memcached servers, such as disabling unnecessary features, securing network connections, and properly managing access controls. 

Lack of built-in encryption: Memcached does not provide built-in encryption for data in transit or at rest. This means that data transmitted over the network or stored in Memcached servers may be susceptible to eavesdropping or unauthorized access. If you need to encrypt data in transit or at rest, you may need to implement additional security measures, such as using SSL/TLS for network encryption or implementing custom encryption/decryption logic in your application. 

Single point of failure: Memcached does not inherently provide high availability or fault tolerance. If a Memcached server fails or becomes unavailable, it can impact the availability and performance of the cached data. It’s important to design your application with appropriate redundancy and failover mechanisms to minimize the impact of a single point of failure in the Memcached infrastructure. 

Amplification attacks: Memcached can be vulnerable to amplification attacks, where an attacker can send a small request to a Memcached server that results in a much larger response being sent to a victim’s IP address. This can be used to amplify the volume of traffic directed at the victim, leading to a Distributed Denial of Service (DDoS) attack. To prevent amplification attacks, it’s important to properly configure Memcached servers to not allow requests from untrusted sources, use firewall rules to restrict access to Memcached servers, and implement rate limiting or other mitigation techniques. 

Data integrity: Memcached does not provide built-in data integrity checks or checksums, which means that data stored in Memcached may be susceptible to corruption or tampering. If data integrity is critical for your application, you may need to implement custom checksums, hash functions, or other integrity validation mechanisms to ensure the integrity of data stored in Memcached. 

Limited data eviction policies: Memcached has limited data eviction policies, which means that when the cache reaches its capacity limit, it may evict data based on its internal algorithms, such as least recently used (LRU) or least frequently used (LFU). This may result in important or frequently accessed data being evicted from the cache, leading to cache misses and reduced performance. It’s important to understand and configure the appropriate data eviction policies in Memcached to ensure optimal cache performance for your specific use case. 

Lack of logging and auditing: Memcached does not provide built-in logging or auditing features, which may make it challenging to track and monitor the activity of Memcached servers. This can make it difficult to identify potential security breaches or unauthorized access. It’s important to implement proper logging and auditing mechanisms in your application or in the infrastructure surrounding Memcached to enable effective monitoring and detection of security incidents. 

Version vulnerabilities: Like any software, Memcached may have known vulnerabilities in specific versions. It’s important to regularly monitor and stay updated with the latest security patches and updates released by the Memcached community. Keeping Memcached and its dependencies up to date with the latest security patches can help mitigate known vulnerabilities. 


1. Secure configuration: Ensure that Memcached servers are properly configured with secure settings, such as disabling external access to Memcached servers, binding to specific IP addresses or interfaces, using authentication mechanisms, and setting appropriate limits for memory usage and item size. Follow best practices for secure configuration as recommended by the Memcached community. 

2. Authentication and authorization: Implement strong authentication and authorization mechanisms for Memcached, such as using SASL (Simple Authentication and Security Layer) to require authentication for clients connecting to Memcached servers and using access control lists (ACLs) to restrict access to trusted sources or specific IP addresses. 

3. Network security: Secure the network communication between Memcached clients and servers by using encryption, such as TLS (Transport Layer Security), to protect against eavesdropping and tampering. Use firewalls and network security groups to restrict incoming and outgoing traffic to only necessary ports and sources. 

4. Patch and update management: Stay updated with the latest security patches and updates released by the Memcached community, and promptly apply them to your Memcached servers to address known vulnerabilities. Regularly monitor security advisories and news related to Memcached to stay informed about potential security risks. 

5. Monitoring and logging: Implement comprehensive monitoring and logging mechanisms for Memcached servers to detect and track suspicious activities, unauthorized access, and potential security breaches. Regularly review and analyze logs to identify any security issues or anomalies. 

6. Data validation and sanitization: Validate and sanitize all data that is stored or retrieved from Memcached to prevent injection attacks, such as SQL injection, command injection, or other code injection attacks. Use safe coding practices and input validation to ensure that only trusted and validated data is stored in Memcached. 

7. Privileged access controls: Limit the access to Memcached servers to only authorized personnel who require it for their legitimate needs. Use role-based access controls (RBAC), least privilege principles, and proper authentication mechanisms to restrict privileged access and prevent unauthorized actions. 

8. Regular security assessments: Conduct regular security assessments and vulnerability scans of your Memcached deployment to identify potential vulnerabilities and weaknesses. Follow industry best practices and security frameworks, such as OWASP (Open Web Application Security Project) guidelines, to ensure a robust and secure configuration of Memcached. 

9. Defense in depth: Implement a layered approach to security, also known as defense in depth, by combining multiple security measures, such as network security, authentication, authorization, encryption, monitoring, logging, and patch management, to provide multiple layers of protection against different types of attacks and reduce the risk of a single point of failure. 


In conclusion, the Memcached protocol is a widely used caching system that provides fast, in-memory data storage and retrieval for web applications. It follows a simple key-value storage model and uses a lightweight, text-based protocol for efficient communication between clients and servers. However, it has some weaknesses and vulnerabilities, including the lack of built-in security features, data consistency, and replication. 

It relies on the trust of clients, which can result in data integrity issues. To mitigate these vulnerabilities, best practices such as implementing proper authentication, securing network communication, and limiting access to trusted clients should be followed. 

Regular monitoring and auditing of Memcached deployments can help detect and address potential security risks. It’s important to understand the weaknesses and vulnerabilities of Memcached and take appropriate measures to secure and protect the data stored in Memcached caches. By implementing proper security measures, Memcached can be used safely and effectively in production environments, enhancing the performance of web applications while safeguarding sensitive data. 

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