CVE-2011-3363 in Linux
Summary
by MITRE
The setup_cifs_sb function in fs/cifs/connect.c in the Linux kernel before 2.6.39 does not properly handle DFS referrals, which allows remote CIFS servers to cause a denial of service (system crash) by placing a referral at the root of a share.
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Analysis
by VulDB Data Team • 03/19/2021
The vulnerability described in CVE-2011-3363 represents a critical denial of service flaw in the Linux kernel's CIFS (Common Internet File System) implementation that affects versions prior to 2.6.39. This issue specifically targets the setup_cifs_sb function within the fs/cifs/connect.c file, which handles the setup of CIFS superblock structures during filesystem mounting operations. The flaw arises from inadequate handling of DFS (Distributed File System) referrals, which are mechanisms used by Windows servers to redirect clients to different servers or locations within a distributed file system architecture. When a remote CIFS server presents a referral at the root level of a share, the vulnerable kernel code fails to properly process this referral structure, leading to a system crash or kernel panic.
The technical exploitation of this vulnerability occurs when a malicious or compromised CIFS server responds to a client connection request with a DFS referral that is positioned at the root of the shared resource. The setup_cifs_sb function lacks proper validation and handling of such referral structures, causing memory corruption or invalid pointer dereferences when attempting to process the referral data. This improper handling triggers a kernel-level fault that results in an immediate system crash, effectively rendering the affected Linux system unavailable to users and applications. The vulnerability is particularly dangerous because it can be triggered remotely without requiring any authentication or privileged access, making it a significant threat to networked systems that may connect to untrusted CIFS servers.
From an operational perspective, this vulnerability creates substantial risk for enterprise environments where Linux systems may connect to various CIFS shares, including those hosted on external or untrusted servers. The denial of service impact extends beyond simple service disruption, as system crashes can lead to data loss, extended downtime, and potential compromise of business continuity. Organizations running Linux kernels version 2.6.38 or earlier are particularly vulnerable, as these systems lack the necessary protections against malformed DFS referral processing. The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and demonstrates how improper input validation in kernel space can lead to system-wide failures. This flaw also maps to ATT&CK technique T1499.004, which covers network denial of service attacks targeting system resources.
The mitigation strategy for CVE-2011-3363 involves upgrading the Linux kernel to version 2.6.39 or later, where the necessary patches have been implemented to properly handle DFS referrals. System administrators should prioritize patching affected systems, particularly those that may connect to external or untrusted CIFS servers. Additional protective measures include implementing network segmentation to limit exposure to potentially malicious CIFS servers, configuring firewalls to restrict CIFS traffic where possible, and monitoring for unusual network activity that might indicate exploitation attempts. Organizations should also consider disabling CIFS mounting capabilities for untrusted networks or implementing additional validation layers at the application level to prevent automatic mounting of potentially malicious CIFS shares. The fix implemented in the patched kernel versions ensures proper validation of DFS referral structures and prevents the kernel from crashing when encountering malformed referral data, thereby maintaining system stability and availability.