CVE-2022-50859: 
Linux Kernel vulnerability analysis and mitigation

CVE-2022-50859 is an information disclosure vulnerability in the Linux kernel's CIFS (Common Internet File System) subsystem, specifically in the handling of the VALIDATE_NEGOTIATE_INFO message. The root cause is a coding error introduced by commit d5c7076b772a ("smb3: add smb3.1.1 to default dialect list"), which extended the dialect count from 3 to 4 but failed to correspondingly reduce the message length, resulting in a message body that is 2 bytes larger than expected and contains uninitialized memory. This uninitialized data may be transmitted over the network, potentially leaking kernel memory contents. Affected kernel versions are those from the introduction of commit d5c7076b772a up to the respective stable-branch fixes. The CVSS category is estimated as Medium, with an EPSS score of approximately 0.024% (Feedly, ENISA EUVD).

The vulnerability is classified under CWE related to use of uninitialized memory / information exposure (information leakage via network). In the Linux kernel's cifs driver, when constructing a VALIDATE_NEGOTIATE_INFO request for SMB3/SMB3.1.1 dialect negotiation, the message length field was not correctly decremented after the dialect list was extended from 3 to 4 entries. As a result, the kernel sends a 28-byte message instead of the correct 26-byte message, with the extra 2 bytes drawn from uninitialized kernel stack or heap memory. This is a local-to-network vector: a system mounting SMB shares using the affected kernel will inadvertently transmit uninitialized memory to the SMB server during the negotiate phase. No authentication or special privileges are required on the attacker's side to receive this leaked data if they control or monitor the SMB server (Feedly, ENISA EUVD).

The primary impact is a confidentiality breach: uninitialized kernel memory (2 bytes per VALIDATE_NEGOTIATE_INFO exchange) may be exposed to a remote SMB server or a network observer. While the leaked data volume per transaction is small, it could potentially contain sensitive kernel memory fragments. Integrity and availability are not directly affected by this vulnerability. The scope is limited to Linux systems actively mounting SMB3/SMB3.1.1 shares using the affected kernel versions (Feedly, ENISA EUVD).

The Linux kernel stable branches have released fixes for this vulnerability. Patched versions include Linux 5.4.220, 5.10.150, 5.15.75, 5.19.17, 6.0.3, and 6.1 (and later). Users should update their Linux kernel to one of these patched versions. As a workaround, administrators can avoid mounting SMB3.1.1 shares on affected systems until a kernel update is applied, or restrict network access to untrusted SMB servers. Amazon Linux 2 users can refer to the ALAS2KERNEL-5.15-2025-090 advisory for distribution-specific guidance (ENISA EUVD, Amazon Linux Advisory).