CVE-2009-1633 in Linux
Summary
by MITRE
Multiple buffer overflows in the cifs subsystem in the Linux kernel before 2.6.29.4 allow remote CIFS servers to cause a denial of service (memory corruption) and possibly have unspecified other impact via (1) a malformed Unicode string, related to Unicode string area alignment in fs/cifs/sess.c; or (2) long Unicode characters, related to fs/cifs/cifssmb.c and the cifs_readdir function in fs/cifs/readdir.c.
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Analysis
by VulDB Data Team • 09/02/2019
The vulnerability identified as CVE-2009-1633 represents a critical security flaw within the Linux kernel's Common Internet File System (CIFS) implementation that affects versions prior to 2.6.29.4. This issue stems from multiple buffer overflow conditions that occur within the kernel's CIFS subsystem, specifically in the handling of Unicode string operations. The vulnerability is particularly concerning because it allows remote attackers to exploit these flaws through malicious CIFS servers, potentially leading to system instability and memory corruption. The CIFS protocol is widely used for file sharing in enterprise environments, making this vulnerability a significant threat to network security infrastructure. The flaw manifests in two distinct attack vectors that target different components of the CIFS subsystem, each presenting unique exploitation pathways that can compromise system integrity.
The technical implementation of this vulnerability involves buffer overflow conditions in two primary files within the Linux kernel source tree. The first vector occurs in fs/cifs/sess.c where Unicode string area alignment is improperly handled, creating opportunities for attackers to manipulate memory layouts through malformed Unicode strings. This particular flaw demonstrates a classic buffer overflow pattern where insufficient bounds checking allows data to overwrite adjacent memory regions. The second vulnerability exists in fs/cifs/cifssmb.c and specifically targets the cifs_readdir function within fs/cifs/readdir.c, where long Unicode characters can trigger memory corruption through improper handling of character sequences. These buffer overflows are classified under CWE-121 as classic stack-based buffer overflow conditions, where insufficient input validation allows attackers to write beyond allocated memory boundaries, potentially corrupting critical kernel data structures.
The operational impact of CVE-2009-1633 extends beyond simple denial of service conditions to potentially enable more sophisticated attacks. When exploited successfully, these buffer overflows can cause memory corruption that may result in system crashes, kernel panics, or unpredictable behavior that could be leveraged for privilege escalation attacks. The vulnerability affects the fundamental file sharing capabilities of Linux systems that utilize CIFS protocols, potentially disrupting business operations in environments where file servers and network shares are critical infrastructure components. Attackers could exploit these conditions to cause persistent denial of service scenarios that would require system rebooting, leading to availability disruptions that could impact enterprise operations and data access. The remote nature of the attack vector means that systems could be compromised without requiring physical access or local user privileges, making this vulnerability particularly dangerous in networked environments.
Mitigation strategies for CVE-2009-1633 primarily focus on immediate kernel version upgrades to 2.6.29.4 or later, which contain the necessary patches to address the buffer overflow conditions. System administrators should implement comprehensive patch management procedures to ensure all affected systems receive updates promptly, as these vulnerabilities are actively exploited in the wild. Network segmentation and firewall rules can help limit exposure by restricting access to CIFS services from untrusted networks, though this approach provides only partial protection given the remote nature of the attack vectors. Additionally, monitoring for unusual CIFS traffic patterns and implementing intrusion detection systems can help identify potential exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1059 (Command and Scripting Interpreter) and T1499 (Endpoint Denial of Service) as attackers may leverage these conditions to establish persistent access or disrupt services. Organizations should also consider implementing kernel hardening measures such as stack canaries and address space layout randomization to make exploitation more difficult, though these measures do not eliminate the vulnerability entirely. Regular security assessments and vulnerability scanning should be conducted to identify systems that may still be running vulnerable kernel versions.