CVE-2020-23356 in Nibbleblog
Summary
by MITRE • 01/28/2021
dmin/kernel/api/login.class.phpin in nibbleblog v3.7.1c 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-2020-23356 resides within the authentication mechanism of nibbleblog version 3.7.1c, specifically in the file admin/kernel/api/login.class.php. This issue represents a classic example of PHP type juggling that can be exploited to bypass authentication controls. The flaw occurs when the application uses the loose comparison operator == instead of the strict comparison operator === when validating password hashes during the login process. This seemingly minor coding oversight creates a significant security weakness that directly impacts the integrity of the authentication system.
The technical exploitation of this vulnerability relies on PHP's type juggling behavior where certain string comparisons can produce unexpected results. When password hashes begin with the string "0e" followed by exclusively numerical characters, PHP interprets these as scientific notation, converting them to the numerical value zero. This happens because PHP's loose comparison operator == performs type coercion, converting the string "0e123456" to the floating point number 0.0, which when compared to another zero value results in a successful match even when the original strings are completely different. This behavior stems from PHP's implicit type conversion rules that can be leveraged to bypass authentication checks.
From an operational perspective, this vulnerability creates a critical risk for systems running affected versions of nibbleblog as it allows unauthorized access to administrative panels without knowledge of valid credentials. Attackers can craft malicious password hashes that will match the stored hash through type juggling, effectively bypassing the entire authentication mechanism. This weakness is particularly dangerous because it can be exploited by any user attempting to log in, potentially leading to complete system compromise including data exfiltration, modification of content, and potential lateral movement within the network. The vulnerability aligns with CWE-501: Trust Boundary Violation and represents a direct violation of secure authentication principles.
The impact of this vulnerability extends beyond simple unauthorized access as it demonstrates poor security practices in input validation and authentication handling. Organizations using affected versions of nibbleblog face significant risk of data breaches and system compromise, particularly in environments where administrative access provides broad control over web applications and associated data. The vulnerability also highlights the importance of implementing strict type checking in security-critical code paths, as recommended by the OWASP Top Ten and NIST cybersecurity guidelines. Mitigation strategies should include immediate patching of the affected software, implementation of strict comparison operators in authentication code, and comprehensive security reviews of all authentication mechanisms to prevent similar type juggling issues from occurring in other parts of the application. The ATT&CK framework categorizes this as a privilege escalation technique through credential access, emphasizing the need for proper input validation and secure coding practices throughout the application lifecycle.