CVE-2004-0949 in Linux
Summary
by MITRE
The smb_recv_trans2 function call in the samba filesystem (smbfs) in Linux kernel 2.4 and 2.6 does not properly handle the re-assembly of fragmented packets correctly, which could allow remote samba servers to (1) read arbitrary kernel information or (2) raise a counter value to an arbitrary number by sending the first part of the fragmented packet multiple times.
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Analysis
by VulDB Data Team • 05/29/2019
The vulnerability described in CVE-2004-0949 represents a critical flaw in the Linux kernel's handling of SMB/CIFS protocol communications through the smbfs filesystem implementation. This issue affects kernel versions 2.4 and 2.6, where the smb_recv_trans2 function fails to properly manage the re-assembly of fragmented network packets during SMB operations. The flaw stems from inadequate validation and processing of packet fragments that are transmitted across the network as part of standard SMB protocol interactions. The vulnerability manifests when remote Samba servers attempt to exploit the improper packet re-assembly logic, creating conditions that can be leveraged for privilege escalation and information disclosure attacks.
The technical implementation of this vulnerability resides in the kernel's network stack processing logic for SMB filesystem operations. When fragmented packets arrive at the smbfs subsystem, the smb_recv_trans2 function does not correctly maintain state information about previously received fragments or properly validate the sequence and integrity of incoming packet data. This improper handling creates two distinct attack vectors: the first allows remote attackers to read arbitrary kernel memory locations by crafting specific fragmented packet sequences that bypass normal access controls. The second vector enables attackers to manipulate internal kernel counters through repeated transmission of the initial fragment of a packet, causing the counter to increment to arbitrarily large values. This counter manipulation can lead to denial of service conditions or potentially enable further exploitation by exhausting kernel resources or corrupting internal data structures.
The operational impact of CVE-2004-0949 extends beyond simple information disclosure to encompass potential privilege escalation and system stability threats. Attackers exploiting this vulnerability can gain access to sensitive kernel memory contents that may contain credentials, session information, or other confidential data that should remain protected within kernel space. The counter manipulation aspect creates a reliable denial of service mechanism that can be used to crash kernel subsystems or render the affected system unstable. Additionally, the vulnerability's presence in both kernel 2.4 and 2.6 versions indicates a widespread exposure across multiple generations of Linux kernel releases, making it particularly dangerous for organizations maintaining legacy systems. This flaw directly relates to CWE-129, which addresses improper validation of the length of input data, and CWE-128, concerning issues with integer underflows or overflows in buffer operations. The vulnerability also aligns with ATT&CK technique T1068, which covers the exploitation of vulnerabilities in kernel-mode components.
Mitigation strategies for CVE-2004-0949 require immediate kernel updates to versions that contain the appropriate patches addressing the packet re-assembly logic in the smbfs subsystem. Organizations should implement network segmentation and access controls to limit exposure of systems running vulnerable kernel versions to trusted networks only. The patch for this vulnerability specifically addresses the improper handling of packet fragment re-assembly by implementing proper validation of fragment sequence numbers and maintaining accurate state information during the re-assembly process. Network monitoring should be enhanced to detect unusual patterns of fragmented packet transmission that may indicate exploitation attempts. System administrators should also consider disabling unused SMB/CIFS services and implementing firewall rules that restrict SMB traffic to necessary communication partners only. The fix typically involves strengthening the validation mechanisms within the smb_recv_trans2 function to ensure that fragment re-assembly occurs correctly and that duplicate or malformed fragments are properly handled without causing kernel memory access violations or counter corruption.