CVE-2020-23361 in PHPList
Summary
by MITRE • 01/28/2021
phpList 3.5.3 allows type juggling for login bypass because == is used instead of === for password hashes, which mishandles hashes that begin with 0e followed by exclusively numerical characters.
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Analysis
by VulDB Data Team • 02/20/2021
The vulnerability identified as CVE-2020-23361 affects phpList version 3.5.3 and represents a critical authentication bypass flaw stemming from improper password hash comparison logic. This issue arises from the use of the loose equality operator == instead of the strict equality operator === when validating user credentials. The flaw specifically targets password hashes that begin with the string 0e followed by exclusively numerical characters, creating a dangerous condition where hash comparisons can be manipulated through type juggling in php's comparison mechanism. When php encounters two values being compared with == and one of them is a string starting with 0e followed by numbers, it attempts to convert the string to a float, treating it as scientific notation. This conversion results in the string being interpreted as 0, which can match other hash values that also convert to zero under the same conditions, effectively bypassing authentication mechanisms.
The technical exploitation of this vulnerability leverages php's type juggling behavior where strings beginning with 0e followed by numeric characters are converted to floating point numbers with a value of zero. This occurs because php interprets 0e123 as 0 times 10 to the power of 123, which equals zero. Attackers can craft malicious password hashes that begin with 0e followed by numeric characters, allowing them to bypass authentication by ensuring their crafted hash value equals zero when converted to float. The vulnerability directly maps to CWE-707, which addresses improper use of insecure or deprecated functions and improper type handling in programming languages. This weakness creates an authentication bypass that can be exploited by any attacker who can influence or predict password hash values, making it particularly dangerous in environments where user accounts can be manipulated or where password reset mechanisms are compromised.
The operational impact of this vulnerability extends beyond simple authentication bypass to potentially enable full system compromise when combined with other attack vectors. An attacker who successfully exploits this vulnerability gains unauthorized access to the phpList application, which can then serve as a foothold for further attacks within the network infrastructure. The vulnerability affects the core authentication system, meaning that all user accounts, administrative functions, and sensitive data within the phpList application become accessible to unauthorized parties. This flaw can be particularly devastating in environments where phpList serves as a critical communication platform for organizations, potentially leading to data breaches, spam distribution, or complete system takeover. The vulnerability also aligns with ATT&CK technique T1110.003, which covers credential stuffing and password guessing attacks, as the flawed comparison logic creates opportunities for attackers to manipulate authentication flows without needing to obtain valid credentials through traditional means.
Mitigation strategies for CVE-2020-23361 require immediate implementation of proper password hash comparison practices throughout the application. The primary fix involves replacing all instances of == with === in password validation logic, ensuring that hash comparisons are performed using strict equality rather than loose equality. Additionally, developers should implement input sanitization and validation for password hashes to prevent manipulation of hash values through type juggling. Organizations should update to phpList version 3.5.4 or later, which contains the necessary patches to address this vulnerability. Security monitoring should be enhanced to detect unusual authentication patterns or attempts to exploit this specific vulnerability. The implementation of proper cryptographic hash functions with appropriate salt values, combined with strict equality checks, will effectively prevent attackers from exploiting this type juggling weakness. Regular security audits should be conducted to identify similar patterns of insecure coding practices that could lead to comparable vulnerabilities in other parts of the application stack.