CVE-2024-23771 in darkhttpd
Summary
by MITRE • 01/22/2024
darkhttpd before 1.15 uses strcmp (which is not constant time) to verify authentication, which makes it easier for remote attackers to bypass authentication via a timing side channel.
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Analysis
by VulDB Data Team • 05/31/2025
The vulnerability identified as CVE-2024-23771 affects darkhttpd versions prior to 1.15 and represents a critical security flaw in the web server's authentication mechanism. This issue stems from the use of the standard strcmp function for password verification, which does not provide constant-time execution characteristics. The implementation creates a timing side channel attack vector that allows remote adversaries to exploit the predictable execution time differences during authentication checks.
The technical flaw manifests when darkhttpd processes HTTP authentication requests using strcmp to compare provided credentials against stored values. Unlike constant-time comparison functions such as memcmp or explicit time-constant string comparison routines, strcmp terminates immediately upon encountering the first mismatched character. This behavior creates measurable timing variations in the server's response time that correlate directly to the number of matching characters in the password attempt. Attackers can leverage this timing differential through repeated authentication attempts to systematically determine the correct password through statistical analysis and timing measurements.
This vulnerability directly maps to CWE-203, which addresses "Observable Behavioral Vulnerability" and specifically targets timing side channels that reveal information about secret values. The operational impact of this flaw extends beyond simple credential theft, as it enables automated password guessing attacks that can systematically bypass authentication mechanisms without requiring direct access to the system. The timing side channel attack operates by measuring the response times of authentication requests and correlating these measurements with password length and character matches, making it particularly dangerous for systems with weak password policies or limited account lockout mechanisms.
The security implications of CVE-2024-23771 align with ATT&CK technique T1212, which focuses on "Exploitation for Credential Access" through timing attacks. This vulnerability can be exploited by remote attackers without requiring any special privileges or local access to the system, making it particularly concerning for publicly accessible web servers. The attack vector allows adversaries to perform automated credential brute force attempts that can succeed even against strong passwords through careful timing analysis and statistical correlation methods.
Organizations using affected versions of darkhttpd should immediately upgrade to version 1.15 or later, which implements constant-time string comparison functions to eliminate the timing side channel. Additional mitigations include implementing rate limiting and account lockout mechanisms to prevent automated attacks, deploying intrusion detection systems to monitor for suspicious authentication patterns, and ensuring that authentication systems use cryptographically secure constant-time comparison functions. The vulnerability demonstrates the critical importance of considering side-channel attacks in security implementations and highlights the necessity of following security best practices such as those outlined in NIST SP 800-57 for cryptographic key management and secure coding practices.