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attack-surface.md

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Attack Surface Analysis for apache/httpd

Attack Surface: Insecure TLS/SSL Configuration

  • Description: Configuration weaknesses in how Apache httpd handles TLS/SSL encryption, leading to compromised confidentiality and integrity of communication. This includes using weak cipher suites, outdated protocols, or improper certificate handling.
  • httpd Contribution: Apache httpd, through modules like mod_ssl or mod_tls, is directly responsible for TLS/SSL implementation and configuration. Misconfigurations here directly expose the server.
  • Example: Apache httpd is configured to use outdated TLS 1.0 protocol and weak cipher suites vulnerable to attacks like BEAST or POODLE. This allows an attacker to decrypt sensitive data transmitted over HTTPS or perform man-in-the-middle attacks.
  • Impact: High. Loss of confidentiality and integrity of sensitive data, man-in-the-middle attacks, eavesdropping on encrypted communications, potential data breaches.
  • Risk Severity: High
  • Mitigation Strategies:
    • Configuration: Strictly configure SSLCipherSuite to use only strong and modern cipher suites (e.g., those offering forward secrecy).
    • Configuration: Disable outdated and insecure protocols like SSLv3, TLS 1.0, and TLS 1.1 using the SSLProtocol directive, enforcing TLS 1.2 and TLS 1.3 only.
    • Configuration: Implement HSTS (HTTP Strict Transport Security) using Header always set Strict-Transport-Security to force HTTPS and prevent protocol downgrade attacks.
    • Regular Updates: Keep mod_ssl or mod_tls and the underlying TLS library (like OpenSSL) updated to the latest versions to patch vulnerabilities.
    • Tools: Regularly test TLS/SSL configuration using online tools and security scanners to identify weaknesses.

Attack Surface: Module Vulnerabilities (Critical Modules)

  • Description: Critical security vulnerabilities found within Apache httpd modules, especially in widely used or core modules. These vulnerabilities can allow for severe exploits like remote code execution or privilege escalation.
  • httpd Contribution: Apache httpd's modular architecture means vulnerabilities in modules directly become vulnerabilities of the web server itself. Critical modules, due to their core functionality or exposure, pose a higher risk.
  • Example: A critical vulnerability is discovered in mod_rewrite that allows an attacker to craft specific rewrite rules leading to buffer overflows and remote code execution on the server.
  • Impact: Critical. Remote code execution, full server compromise, data breaches, denial of service, privilege escalation, complete loss of confidentiality, integrity, and availability.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Principle of Least Privilege: Disable any modules that are not absolutely essential for the application's functionality to reduce the attack surface.
    • Regular Updates: Implement a rigorous patch management process to immediately apply security updates for Apache httpd and all enabled modules as soon as they are released.
    • Security Monitoring: Monitor security mailing lists and vulnerability databases for announcements of new vulnerabilities in Apache httpd modules.
    • Vulnerability Scanning: Regularly use vulnerability scanners to detect known vulnerabilities in the installed Apache httpd and its modules.

Attack Surface: HTTP Request Smuggling

  • Description: Exploiting inconsistencies in how Apache httpd parses and processes HTTP requests compared to front-end proxies or other intermediary devices. This allows attackers to "smuggle" malicious requests that bypass security controls and are processed directly by httpd.
  • httpd Contribution: Vulnerabilities in Apache httpd's HTTP parsing logic, especially when handling edge cases or complex request structures, can make it susceptible to request smuggling attacks.
  • Example: An attacker crafts a specially formatted HTTP request that is interpreted as two separate requests by Apache httpd, while a front-end proxy only sees one. This allows the attacker to bypass proxy-level authentication or access controls and inject malicious requests directly to the application behind httpd.
  • Impact: High. Security bypass, unauthorized access to restricted resources, potential for cross-site scripting (XSS), cache poisoning, session hijacking, and other severe attacks.
  • Risk Severity: High
  • Mitigation Strategies:
    • Configuration: Ensure consistent HTTP parsing behavior between front-end proxies and Apache httpd. Carefully review proxy configurations and httpd configurations for potential discrepancies.
    • Configuration: Disable or carefully configure features that might contribute to request smuggling, such as handling of chunked encoding and connection keep-alive.
    • Regular Updates: Keep Apache httpd updated to the latest version to patch known request smuggling vulnerabilities.
    • Web Application Firewall (WAF): Deploy a WAF capable of detecting and mitigating HTTP request smuggling attacks.

Attack Surface: Denial of Service (DoS) - Resource Exhaustion Attacks

  • Description: Attacks that exploit Apache httpd's resource handling to exhaust server resources (CPU, memory, connections, bandwidth), leading to service disruption and unavailability for legitimate users. This includes attacks like Slowloris and more general resource exhaustion through malformed requests.
  • httpd Contribution: Apache httpd's design and resource management mechanisms can be targeted by DoS attacks if not properly configured and protected.
  • Example (Resource Exhaustion): An attacker sends a large volume of specially crafted HTTP requests with excessively large headers or bodies, causing Apache httpd to consume excessive memory and CPU resources, eventually leading to server overload and crash.
  • Impact: High. Service disruption, website unavailability, financial losses, damage to reputation.
  • Risk Severity: High
  • Mitigation Strategies:
    • Configuration: Implement resource limits within Apache httpd configuration, such as LimitRequestFields, LimitRequestLine, LimitRequestBody, Timeout, and connection limits.
    • Operating System Limits: Configure operating system level limits on resources like open files and connections to further restrict resource consumption.
    • Rate Limiting: Implement rate limiting mechanisms (e.g., using mod_ratelimit or a WAF) to restrict the number of requests from a single IP address within a given timeframe.
    • Load Balancing and DDoS Mitigation Services: Utilize load balancers to distribute traffic and DDoS mitigation services to filter malicious traffic and absorb large-scale attacks.
    • Regular Monitoring: Monitor server resource usage (CPU, memory, network) to detect and respond to DoS attacks in progress.

Attack Surface: Insecure Access Control Configuration Leading to Critical Resource Exposure

  • Description: Misconfiguration of Apache httpd's access control mechanisms (using <Directory>, <Location>, .htaccess, Require directives) that results in unauthorized access to critical resources, sensitive data, or administrative functionalities.
  • httpd Contribution: Apache httpd provides the framework and directives for access control. Misconfiguration within these directives directly leads to access control vulnerabilities within the web server.
  • Example: A <Directory> block intended to restrict access to an administrative backend is misconfigured, accidentally allowing public access without authentication. This exposes sensitive administrative functionalities and potentially allows attackers to compromise the entire application.
  • Impact: High to Critical. Unauthorized access to sensitive data, administrative panels, or critical application functionalities. Can lead to data breaches, full application compromise, and remote code execution if administrative interfaces are vulnerable.
  • Risk Severity: High to Critical (depending on the sensitivity of exposed resources)
  • Mitigation Strategies:
    • Configuration Review and Auditing: Thoroughly review and audit all access control configurations in httpd.conf, virtual host configurations, and .htaccess files.
    • Principle of Least Privilege: Implement access control rules based on the principle of least privilege, granting only the necessary access to specific users or groups. Deny access by default and explicitly allow only when required.
    • Centralized Configuration: Prefer managing access control in the main httpd.conf or virtual host files for better oversight and control, minimizing reliance on distributed .htaccess files.
    • Testing and Validation: Thoroughly test access control rules after implementation and changes to ensure they function as intended and prevent unintended access.
    • Regular Security Assessments: Include access control configuration review as part of regular security assessments and penetration testing.