CVE-2022-50856: 
Linux Kernel vulnerability analysis and mitigation

CVE-2022-50856 is a resource leak vulnerability in the Linux kernel's CIFS (Common Internet File System) subsystem. Specifically, the function cifs_ses_add_channel() fails to free an xid (transaction ID) before returning, resulting in an xid leak. The vulnerability affects Linux kernel versions starting from the commit introducing the bug (d70e9fa55884760b6d6c293dbf20d8c52ce11fb7) up to the patched releases. Fixed versions include kernel 5.10.152, 5.15.76, 6.0.6, and 6.1. It was published on December 30, 2025, and carries an estimated CVSS severity of Medium (Feedly, ENISA EUVD).

The root cause is a missing resource deallocation (CWE-401: Missing Release of Memory after Effective Lifetime) in the cifs_ses_add_channel() function within the Linux kernel's CIFS driver. When the function returns — whether on success or error paths — it does not call the appropriate free_xid() to release the transaction ID allocated at the start of the function. This results in a kernel-level resource leak where xid slots are exhausted over time if the code path is triggered repeatedly. The fix, applied across multiple stable branches, ensures free_xid() is called before all return paths (Feedly, ENISA EUVD).

The primary impact of this vulnerability is a kernel resource leak that can degrade system stability over time. Repeated triggering of the affected code path — for example, by establishing multiple SMB multichannel sessions — can exhaust available xid slots, potentially leading to denial of service conditions or degraded CIFS/SMB functionality. There is no known confidentiality or integrity impact; the vulnerability is limited to availability (Feedly).

The Linux kernel maintainers have released patches across multiple stable branches. Users should upgrade to kernel version 5.10.152 or later (5.10.x branch), 5.15.76 or later (5.15.x branch), 6.0.6 or later (6.0.x branch), or 6.1 or later. The fix ensures free_xid() is called on all return paths within cifs_ses_add_channel(). Linux distribution vendors (e.g., Red Hat, Ubuntu, SUSE) are expected to backport this fix into their respective kernel packages; users should apply available distribution security updates (ENISA EUVD, Feedly).