CVE-2009-1384 in Pam-krb5
Summary
by MITRE
pam_krb5 2.2.14 through 2.3.4, as used in Red Hat Enterprise Linux (RHEL) 5, generates different password prompts depending on whether the user account exists, which allows remote attackers to enumerate valid usernames.
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Analysis
by VulDB Data Team • 03/30/2025
The vulnerability identified as CVE-2009-1384 affects the pam_krb5 module version 2.2.14 through 2.3.4 in Red Hat Enterprise Linux 5 systems. This issue stems from the module's improper handling of authentication prompts during the Kerberos authentication process, creating a timing-based side-channel attack vector that reveals information about user account existence. The flaw specifically manifests when the module generates different password prompt messages depending on whether the target user account exists in the system's user database.
The technical implementation of this vulnerability exploits a fundamental weakness in the authentication flow where pam_krb5 responds differently to authentication attempts based on user account existence. When a user attempts to authenticate with a non-existent account, the module generates a prompt indicating that the account does not exist, whereas for valid accounts, it prompts for the password without any account existence verification message. This differential response creates a predictable pattern that attackers can exploit to determine which usernames are valid within the system. The vulnerability operates at the authentication module level within the Pluggable Authentication Modules framework, which is a critical component of the Linux authentication infrastructure and is referenced under CWE-200 as "Information Exposure Through Side-Channel Timing" and CWE-305 as "Authentication Bypass Using Alternate Access Method."
The operational impact of this vulnerability extends beyond simple user enumeration, as it provides attackers with valuable reconnaissance information that can be leveraged in subsequent attack phases. An attacker can systematically test usernames against the authentication service, using the different prompt responses to identify valid accounts within the Kerberos realm. This enumeration capability significantly reduces the complexity of brute force attacks and password guessing attempts, as attackers can focus their efforts on known valid accounts rather than randomly guessing credentials. The vulnerability particularly affects systems where Kerberos authentication is used for single sign-on services, which are common in enterprise environments where user account management and authentication are centralized. According to ATT&CK framework technique T1078.001, this vulnerability enables adversaries to establish persistence by identifying valid accounts, while T1565.001 describes how this information can be used for credential access and privilege escalation.
Mitigation strategies for CVE-2009-1384 require immediate patching of the pam_krb5 module to a version that implements consistent authentication prompt behavior regardless of account existence. System administrators should ensure that all RHEL 5 systems are updated to the latest available pam_krb5 package that resolves this issue, as the vulnerability affects the core authentication infrastructure. Additionally, implementing proper account lockout policies and rate limiting mechanisms can help reduce the effectiveness of automated enumeration attacks. Organizations should also consider implementing network-based controls such as firewall rules that limit access to authentication services from unauthorized networks, and monitoring systems that can detect unusual authentication patterns that may indicate enumeration attempts. The vulnerability highlights the importance of consistent error handling and response generation in authentication modules, as specified in security standards that emphasize the need for uniform responses to prevent information leakage through side-channel attacks.