threat-modeling.md

Threat Model Analysis for egulias/emailvalidator

Threat: Regular Expression Denial of Service (ReDoS) - Elevated Severity

Description: An attacker crafts a highly specific and malicious email address string that exploits vulnerable regular expression patterns used within emailvalidator for email validation. By submitting this crafted input, the attacker can force the regex engine to perform excessive backtracking and computations, leading to a significant increase in CPU usage and a potential Denial of Service (DoS) condition. This attack is directly triggered by the regex patterns within emailvalidator's code. Impact:

• Severe application slowdown, potentially making the application unusable for legitimate users.
• Service disruption or temporary unavailability due to resource exhaustion, potentially requiring manual intervention to restore service.
• Potential for cascading failures if other application components depend on the resources exhausted by the ReDoS attack. Affected Component: Regular expression patterns within the Validation module and validator classes, specifically within functions responsible for regex matching of email address components (e.g., local part, domain part). Risk Severity: High Mitigation Strategies:
• Review and Harden Regex Patterns (Contribute to emailvalidator): If possible and you have expertise in regular expressions and security, examine the emailvalidator library's source code to identify and analyze the regex patterns used for validation. Look for patterns known to be susceptible to ReDoS and consider contributing improved, more robust regex patterns to the library project.
• Implement Validation Timeouts: Crucially, set strict timeouts for email validation operations within your application. This prevents any single validation attempt, especially those triggered by malicious ReDoS inputs, from consuming excessive resources indefinitely. If validation exceeds the timeout, terminate the process.
• Apply Rate Limiting: Implement rate limiting on email validation requests at the application level. This restricts the number of validation attempts from a single IP address or user within a given timeframe, mitigating the impact of automated ReDoS attacks.
• Monitor CPU Usage: Implement monitoring of CPU usage on servers running the application. Sudden spikes in CPU usage during email validation processes could be an indicator of a ReDoS attack attempt, allowing for faster incident response.
• Stay Updated and Monitor Security Advisories: Keep emailvalidator updated to the latest version. Monitor security advisories and the emailvalidator project's issue tracker for reports of ReDoS vulnerabilities and apply patches promptly when available.