CVE-2023-40765 in Event Booking Calendar
Summary
by MITRE • 08/28/2023
User enumeration is found in PHPJabbers Event Booking Calendar v4.0. This issue occurs during password recovery, where a difference in messages could allow an attacker to determine if the user is valid or not, enabling a brute force attack with valid users.
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Analysis
by VulDB Data Team • 01/28/2026
The vulnerability identified as CVE-2023-40765 represents a critical user enumeration flaw within PHPJabbers Event Booking Calendar version 4.0 that significantly undermines the application's security posture. This issue manifests specifically during the password recovery process where the system provides distinguishable response messages to users, creating a side-channel attack vector that adversaries can exploit to identify valid user accounts. The flaw stems from the application's failure to implement consistent error messaging regardless of whether a user account exists in the system, thereby leaking information about the validity of submitted usernames through subtle variations in response behavior.
From a technical perspective, this vulnerability aligns with CWE-200, which addresses the disclosure of information to unauthorized actors, and represents a classic example of information leakage through response differentiation. The attack mechanism operates by systematically submitting various usernames to the password recovery endpoint and analyzing the responses for subtle timing differences or message variations that indicate whether the submitted username corresponds to an existing account. This enumeration capability transforms what would otherwise be a brute force attack against a random set of credentials into a targeted assault focused specifically on valid user accounts, dramatically reducing the attack surface and increasing success probability.
The operational impact of this vulnerability extends beyond simple credential theft, as it enables attackers to build comprehensive user directories that can be leveraged for subsequent attacks including targeted phishing campaigns, account takeover attempts, and social engineering operations. The vulnerability particularly affects organizations that rely on the Event Booking Calendar for managing event registrations and user data, where the exposure of valid user accounts could lead to unauthorized access to sensitive event information, attendee data, and potentially broader system access if the calendar application shares user databases with other systems. The implications are further amplified when considering that many organizations implement weak password policies or reuse credentials across systems, making the enumeration of valid users a gateway to more extensive compromise.
Security professionals should implement multiple layers of mitigation to address this vulnerability effectively. The primary remediation involves standardizing all password recovery responses to provide identical messaging regardless of whether the user account exists, ensuring that the system behaves consistently for both valid and invalid inputs. Additionally, implementing rate limiting and account lockout mechanisms during password recovery attempts can significantly hinder automated enumeration attacks. Organizations should also consider implementing CAPTCHA systems or other authentication challenges to further prevent automated exploitation. The solution approach aligns with ATT&CK technique T1078.004 which addresses valid accounts and T1110 which covers credential access through brute force methods. Regular security testing and code reviews should be implemented to identify similar information leakage vulnerabilities in other application components, as this type of flaw often indicates broader architectural weaknesses in security design. The remediation process should also include comprehensive logging and monitoring to detect suspicious patterns of enumeration attempts that may indicate ongoing attacks against the system.