CVE-2014-3493 in Samba
Summary
by MITRE
The push_ascii function in smbd in Samba 3.6.x before 3.6.24, 4.0.x before 4.0.19, and 4.1.x before 4.1.9 allows remote authenticated users to cause a denial of service (memory corruption and daemon crash) via an attempt to read a Unicode pathname without specifying use of Unicode, leading to a character-set conversion failure that triggers an invalid pointer dereference.
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Analysis
by VulDB Data Team • 08/01/2021
The vulnerability described in CVE-2014-3493 represents a critical memory corruption issue within the Samba file sharing implementation that affects multiple versions of the software. This flaw exists in the push_ascii function within smbd, which is the primary daemon responsible for handling SMB/CIFS file sharing operations in Samba. The vulnerability specifically targets the handling of Unicode pathnames when the client does not explicitly specify Unicode usage, creating a scenario where character-set conversion failures can occur. This issue impacts Samba versions 3.6.x prior to 3.6.24, 4.0.x prior to 4.0.19, and 4.1.x prior to 4.1.9, making it a widespread concern across several major release branches.
The technical mechanism of this vulnerability involves a classic invalid pointer dereference condition that arises during character encoding conversion processes. When an authenticated remote attacker attempts to read a Unicode pathname without explicitly declaring Unicode usage, the system's character-set conversion logic fails to properly handle the transition between different encoding formats. This failure results in memory corruption that manifests as an invalid pointer dereference, ultimately causing the smbd daemon to crash and restart. The flaw occurs because the push_ascii function does not adequately validate or handle cases where Unicode pathnames are processed without proper Unicode context, leading to memory management issues that can be exploited to trigger a denial of service condition.
From an operational impact perspective, this vulnerability provides attackers with a reliable method to disrupt Samba services through a denial of service attack. The fact that remote authenticated users can exploit this issue means that legitimate users who have access to the Samba service can intentionally cause service interruptions that affect all other users of the system. This vulnerability directly violates the availability principle of the CIA triad and can be particularly damaging in enterprise environments where Samba serves as a critical file sharing infrastructure. The daemon crash that results from this exploitation can lead to temporary unavailability of shared resources, potentially causing business disruption and requiring manual intervention to restore service.
The vulnerability aligns with CWE-476, which describes NULL pointer dereferences, and demonstrates how improper handling of character encoding scenarios can lead to memory corruption issues. This flaw also maps to ATT&CK technique T1499.004, which covers network denial of service attacks through service interruption. Organizations using affected Samba versions face significant risk as this vulnerability can be exploited without requiring special privileges beyond authentication, making it accessible to any user with valid credentials to the Samba service. The exploitation process is straightforward and reliable, making this a preferred target for attackers seeking to disrupt file sharing services.
Mitigation strategies for CVE-2014-3493 primarily focus on applying the official security patches released by the Samba project. System administrators should immediately upgrade to Samba versions 3.6.24, 4.0.19, or 4.1.9 and later, which contain the necessary fixes for this memory corruption issue. Additionally, network segmentation and access controls should be implemented to limit the number of authenticated users who can access Samba services, reducing the attack surface. Monitoring systems should be configured to detect unusual patterns of service restarts or daemon crashes that could indicate exploitation attempts. Organizations should also consider implementing intrusion detection systems that can identify suspicious SMB traffic patterns associated with this specific vulnerability. The patch implementation should be prioritized as a critical security update, particularly in environments where Samba serves as a primary file sharing infrastructure and where service availability is critical to business operations.