CVE-2021-36716 in is-email Package
Summary
by MITRE • 07/15/2021
A ReDoS (regular expression denial of service) flaw was found in the Segment is-email package before 1.0.1 for Node.js. An attacker that is able to provide crafted input to the isEmail(input) function may cause an application to consume an excessive amount of CPU.
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Analysis
by VulDB Data Team • 07/18/2021
The vulnerability identified as CVE-2021-36716 represents a classic regular expression denial of service flaw within the Segment is-email package for Node.js. This issue affects versions prior to 1.0.1 and demonstrates how seemingly benign input validation functions can become critical attack vectors when poorly implemented regular expressions are employed. The flaw resides in the isEmail(input) function which processes email address validation through regular expression patterns that are susceptible to catastrophic backtracking behavior.
The technical implementation of this vulnerability stems from the use of inefficient regular expressions that exhibit exponential time complexity when processing maliciously crafted input strings. When an attacker provides carefully constructed input that matches the pattern of the vulnerable regex, the regular expression engine enters into a state of catastrophic backtracking where it repeatedly attempts different matching paths, leading to exponential CPU consumption. This behavior directly maps to CWE-1333 which specifically addresses inefficient regular expression complexity, and represents a fundamental flaw in the regular expression design that allows for predictable performance degradation under adversarial input conditions.
From an operational perspective, this vulnerability poses significant risks to applications that rely on email validation as part of their input processing workflows. The impact extends beyond simple performance degradation to potentially enabling full denial of service conditions where legitimate users cannot access services due to excessive CPU consumption by the validation process. Applications utilizing the affected package may experience complete service unavailability during attack windows, particularly in high-traffic scenarios where multiple validation requests are processed concurrently. The vulnerability can be exploited through various attack vectors including web forms, API endpoints, and any input mechanism that validates email addresses, making it particularly dangerous in multi-layered attack scenarios.
Mitigation strategies for CVE-2021-36716 should prioritize immediate package updates to version 1.0.1 or later where the regular expression implementation has been corrected to prevent catastrophic backtracking. Organizations should also implement input validation rate limiting and monitoring to detect unusual CPU consumption patterns that may indicate exploitation attempts. Additionally, the implementation of alternative email validation approaches using more efficient regex patterns or dedicated validation libraries can provide additional defense-in-depth. This vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks through resource exhaustion, and organizations should consider implementing network-level protections such as rate limiting and traffic shaping to mitigate potential exploitation attempts.