1. Introduction
memcached Detection identifies instances where the memcached caching system is running on a network port. Memcached, while useful for improving application performance, can be exploited if exposed to untrusted networks. This affects servers hosting applications that use memcached for session management or data caching. A successful exploit could lead to information disclosure and potential remote code execution. Confidentiality, integrity, and availability may all be impacted.
2. Technical Explanation
The vulnerability arises from memcached listening on a network port without authentication enabled by default. This allows any system that can reach the port to send commands to the server. Attackers can use these commands to retrieve data stored in the cache, potentially including sensitive information like session tokens or API keys. There is no known CVE associated with this detection as it represents a configuration issue rather than a software flaw.
- Root cause: memcached listens on a network port without SASL authentication enabled by default.
- Exploit mechanism: An attacker sends commands to the exposed memcached instance, requesting data stored in the cache. A simple example is using telnet or netcat to connect to the port and issue ‘stats items’ to retrieve cached item statistics.
- Scope: Affected platforms are any operating systems (Linux, Windows, macOS) running a memcached server version prior to configuration changes.
3. Detection and Assessment
You can confirm if a system is vulnerable by checking for an open port associated with the memcached service. A thorough method involves attempting to retrieve data from the cache.
- Quick checks: Use `netstat -tulnp | grep memcached` or `ss -tulnp | grep memcached` on Linux systems to identify if memcached is listening on a port.
- Scanning: Nessus plugin ID 16234 can detect exposed memcached instances. OpenVAS also has relevant checks. These are examples only and may require updates.
- Logs and evidence: Memcached logs typically do not record connection attempts, so network traffic analysis is the primary source of evidence. Look for connections to port 11211 (default) from unexpected sources.
netstat -tulnp | grep memcached4. Solution / Remediation Steps
The following steps restrict access to the memcached service, reducing the risk of exploitation.
4.1 Preparation
- Ensure you have SSH access and appropriate permissions to modify the memcached configuration file. A roll back plan involves restoring from the snapshot or restarting the application with the original configuration.
- A change window may be required depending on service criticality, and approval from the application owner is recommended.
4.2 Implementation
- Step 1: Edit the memcached configuration file (usually /etc/memcached.conf or similar).
- Step 2: Add the line `-S` to enable SASL authentication.
- Step 3: Configure SASL users and passwords using a suitable method, such as `authplain`.
- Step 4: Restart the memcached service.
4.3 Config or Code Example
Before
# /etc/memcached.conf
port 11211
After
# /etc/memcached.conf
port 11211
-S
authplain on
sasl_username youruser
sasl_password yourpassword
4.4 Security Practices Relevant to This Vulnerability
Several security practices can help prevent this issue.
- Practice 1: Least privilege – only allow necessary services to bind to network ports, and restrict access using firewalls or authentication.
- Practice 2: Secure defaults – configure all services with the most secure settings by default, including requiring authentication where possible.
4.5 Automation (Optional)
Ansible can be used to automate configuration changes.
---
- name: Enable SASL for memcached
hosts: all
become: true
tasks:
- lineinfile:
path: /etc/memcached.conf
regexp: '^port'
line: 'port 11211'
- lineinfile:
path: /etc/memcached.conf
insertafter: '^port'
line: '-S'
- lineinfile:
path: /etc/memcached.conf
insertafter: '-S'
line: 'authplain on'
- service:
name: memcached
state: restarted
5. Verification / Validation
Confirm the fix by checking that SASL authentication is enabled and that unauthorized access is blocked.
- Post-fix check: Use `netstat -tulnp | grep memcached` to confirm the service is running, then attempt to connect using telnet without providing credentials. You should receive an error message indicating authentication is required.
- Re-test: Re-run the initial netcat command and verify that it no longer returns cached data without valid SASL credentials.
- Monitoring: Monitor memcached logs for failed authentication attempts, which could indicate unauthorized access attempts.
netstat -tulnp | grep memcached6. Preventive Measures and Monitoring
Update security baselines to include requirements for secure memcached configuration.
- Baselines: Update your security baseline or CIS control implementation to require SASL authentication for all memcached instances.
- Pipelines: Include checks in CI/CD pipelines to ensure that the memcached configuration file does not contain insecure settings, such as missing SASL authentication.
- Asset and patch process: Review memcached configurations regularly (e.g., quarterly) as part of your asset management and patching process.
7. Risks, Side Effects, and Roll Back
Enabling SASL may require changes to applications that connect to memcached.
- Risk or side effect 1: Applications using memcached may need to be updated with valid credentials.
- Risk or side effect 2: Incorrect SASL configuration could prevent legitimate applications from connecting.
- Roll back: Restore the original memcached configuration file and restart the service.
8. References and Resources
Link only to sources that match this exact vulnerability.
- Vendor advisory or bulletin: http://memcached.org/
- NVD or CVE entry: Not applicable, as this is a configuration issue.
- Product or platform documentation relevant to the fix: https://www.mediawiki.org/wiki/Memcached