CVE-2019-14833 in Samba
Summary
by MITRE
A flaw was found in Samba, all versions starting samba 4.5.0 until samba 4.9.15, samba 4.10.10, samba 4.11.2, in the way it handles a user password change or a new password for a samba user. The Samba Active Directory Domain Controller can be configured to use a custom script to check for password complexity. This configuration can fail to verify password complexity when non-ASCII characters are used in the password, which could lead to weak passwords being set for samba users, making it vulnerable to dictionary attacks.
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Analysis
by VulDB Data Team • 02/05/2024
The vulnerability identified as CVE-2019-14833 represents a critical weakness in Samba's password validation mechanism that affects versions from 4.5.0 through 4.9.15, 4.10.10, and 4.11.2. This flaw specifically targets the Active Directory Domain Controller implementation within Samba, where administrators can configure custom scripts to enforce password complexity requirements. The issue manifests when Samba processes password changes or new password assignments for users, creating a scenario where the system fails to properly validate password strength when non-ascii characters are present in the password string. This vulnerability operates at the intersection of authentication security and input validation, fundamentally undermining the password policy enforcement capabilities of Samba implementations.
The technical nature of this vulnerability stems from improper handling of character encoding during password validation processes. When non-ascii characters are included in passwords, the custom password complexity scripts fail to correctly parse or evaluate these characters against established complexity requirements. This creates a condition where attackers can bypass password strength checks by incorporating non-ascii characters into their passwords, effectively rendering the configured complexity policies ineffective. The flaw can be categorized under CWE-257 as a weakness in password management, specifically involving the improper handling of password validation logic. This vulnerability directly impacts the principle of least privilege and authentication security by allowing weak passwords to be accepted, potentially enabling unauthorized access through dictionary attacks or brute force methods.
The operational impact of CVE-2019-14833 extends beyond simple password validation failures to create significant security risks for organizations relying on Samba for Active Directory services. When weak passwords are accepted due to the bypass mechanism, it dramatically increases the attack surface for credential-based attacks, particularly dictionary attacks that target common password patterns. The vulnerability essentially creates a backdoor for attackers to circumvent security controls, as the system's own password policy enforcement mechanisms become ineffective against non-ascii character inputs. Organizations using Samba AD domain controllers may experience unauthorized access to user accounts, privilege escalation opportunities, and potential domain compromise. This weakness aligns with ATT&CK technique T1110.003 for credential stuffing and password spraying attacks, as the vulnerability makes it easier for attackers to discover valid credentials through automated means.
Mitigation strategies for this vulnerability require immediate patching of affected Samba versions to the latest stable releases that contain the fix for the password validation logic. Organizations should also implement additional security controls such as account lockout policies, multi-factor authentication, and regular security audits of password policies to detect potential exploitation. System administrators should review and test custom password complexity scripts to ensure they properly handle all character sets, including non-ascii characters. The fix for this vulnerability addresses the root cause by ensuring proper character encoding handling during password validation, preventing the bypass of complexity requirements that occurs with non-ascii inputs. Security monitoring should be enhanced to detect unusual password change patterns or rapid attempts to set weak passwords, as these activities may indicate exploitation attempts. Organizations should also consider implementing password policies that explicitly prohibit the use of non-ascii characters in passwords, though this approach requires careful consideration of legitimate user needs and accessibility requirements.