CVE-2015-7686 in Address.pm
Summary
by MITRE
Algorithmic complexity vulnerability in Address.pm in the Email-Address module 1.908 and earlier for Perl allows remote attackers to cause a denial of service (CPU consumption) via a crafted string containing a list of e-mail addresses in conjunction with parenthesis characters that can be associated with nested comments. NOTE: the default configuration in 1.908 mitigates this vulnerability but misparses certain realistic comments.
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Analysis
by VulDB Data Team • 06/20/2022
The CVE-2015-7686 vulnerability represents a critical algorithmic complexity flaw within the Email-Address Perl module version 1.908 and earlier, specifically affecting the Address.pm component responsible for parsing email addresses. This vulnerability manifests as a denial of service condition that can be triggered remotely through carefully crafted input strings containing email addresses with nested parentheses that form comment structures. The flaw exploits the module's inefficient parsing algorithm that exhibits exponential time complexity when processing malformed email address strings with deeply nested parentheses, leading to excessive cpu consumption and system resource exhaustion.
The technical implementation of this vulnerability stems from the module's recursive parsing approach that fails to properly handle nested comment structures within email addresses. When the parser encounters a string containing email addresses with nested parentheses, it enters into a computationally expensive backtracking process that grows exponentially with the depth of nesting. This behavior creates a classic algorithmic complexity attack vector where the computational resources required to process the input increase dramatically with input complexity. The vulnerability operates at the parsing layer of email address validation, making it particularly dangerous as it can be exploited through any application that utilizes the affected Email-Address module for email validation or processing. The flaw aligns with CWE-400, which categorizes excessive computational complexity as a security weakness, and represents a specific instance of resource exhaustion through algorithmic complexity attacks.
The operational impact of this vulnerability extends beyond simple denial of service to potentially compromise entire applications or systems that rely on email address validation. Attackers can craft malicious email address strings that cause the target application to consume excessive cpu cycles, leading to service unavailability for legitimate users. This vulnerability affects applications across various domains including web applications, email servers, and any system that validates email addresses through the affected Perl module. The exploitation is particularly concerning because it requires minimal input complexity to generate significant computational overhead, making it an attractive attack vector for resource exhaustion attacks. The vulnerability also demonstrates the importance of proper input validation and the potential for seemingly benign parsing operations to become security threats when algorithmic complexity is not properly controlled.
The default configuration in version 1.908 provides a partial mitigation by limiting the depth of nested parentheses that can be processed, but this approach introduces a new problem of misparsing legitimate email comments that contain nested structures. This trade-off between security and functionality creates a challenging scenario for system administrators who must balance protection against denial of service attacks with maintaining compatibility with valid email address formats. The vulnerability highlights the need for robust algorithmic complexity controls in parsing libraries and demonstrates how seemingly simple parsing operations can become security risks when not properly constrained. Organizations should implement proper input sanitization, set resource limits on parsing operations, and regularly update their Perl modules to versions that address this specific vulnerability. The issue also underscores the importance of following security guidelines such as those provided by the Open Web Application Security Project and aligns with ATT&CK technique T1496, which covers resource exhaustion attacks through algorithmic complexity. System administrators should monitor for applications using vulnerable versions of the Email-Address module and ensure that all systems are updated to patched versions that properly handle nested comment structures without exposing the underlying algorithmic complexity vulnerabilities.