CVE-2011-3191 in Linux
Summary
by MITRE
Integer signedness error in the CIFSFindNext function in fs/cifs/cifssmb.c in the Linux kernel before 3.1 allows remote CIFS servers to cause a denial of service (memory corruption) or possibly have unspecified other impact via a large length value in a response to a read request for a directory.
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Analysis
by VulDB Data Team • 03/19/2021
The vulnerability identified as CVE-2011-3191 represents a critical integer signedness error within the Linux kernel's CIFS (Common Internet File System) implementation. This flaw exists in the CIFSFindNext function located in fs/cifs/cifssmb.c and affects Linux kernel versions prior to 3.1. The vulnerability stems from improper handling of signed and unsigned integer values during directory read operations, creating a condition where malicious CIFS servers can manipulate response data to exploit the kernel's memory management subsystem.
The technical exploitation of this vulnerability occurs when a remote CIFS server responds to a directory read request with a specially crafted response containing an excessively large length value. The kernel's CIFS implementation fails to properly validate or convert this value, leading to a scenario where a signed integer is treated as unsigned during memory allocation or buffer handling operations. This mismatch causes the kernel to allocate insufficient memory or compute incorrect buffer boundaries, resulting in memory corruption that can manifest as kernel panics, system crashes, or more subtle memory management issues. The flaw operates at the intersection of kernel-level networking protocols and memory management, making it particularly dangerous as it can be triggered remotely without requiring local access.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enabling more sophisticated attacks. While the primary effect is memory corruption and system instability, the underlying integer overflow condition creates opportunities for privilege escalation or information disclosure depending on the specific memory corruption patterns. Attackers can leverage this vulnerability to cause persistent system downtime, disrupt network services, or potentially establish footholds within networked environments where CIFS shares are actively used. The vulnerability affects systems that mount CIFS shares from remote servers, making it particularly concerning for enterprise environments where file sharing protocols are commonly deployed.
Mitigation strategies for CVE-2011-3191 focus on both immediate patching and operational security measures. The primary solution involves upgrading to Linux kernel version 3.1 or later where the integer signedness error has been corrected through proper input validation and type conversion mechanisms. Organizations should also implement network segmentation to limit exposure of systems to untrusted CIFS servers, disable unnecessary CIFS mounting capabilities, and monitor for suspicious network traffic patterns that might indicate exploitation attempts. Security teams should consider implementing intrusion detection systems that can identify malformed CIFS responses and establish baseline network behavior to detect anomalous directory read operations. This vulnerability aligns with CWE-191, which addresses integer underflow and overflow conditions, and relates to ATT&CK techniques involving privilege escalation and denial of service through kernel exploitation. The vulnerability demonstrates how seemingly minor implementation details in kernel networking code can create significant security risks that affect the entire system stability and potentially enable broader compromise scenarios.