The Linux kernel's ksmbd module had a memory leak vulnerability (CVE-2026-64139) in the set_posix_acl_entries_dacl() function. A recent commit introduced overflow checks that break out of loops when the accumulated DACL size would overflow a 16-bit limit. However, these breaks bypass the kfree() calls responsible for releasing allocated struct smb_sid objects, causing a memory leak. An attacker can exploit this by crafting files with enough POSIX ACL entries to trigger the overflow, leaking kernel memory on each access to the file's DACL. The vulnerability allows trivial kernel memory exhaustion. The patch fixes this by ensuring the sid memory is freed before breaking out of the loops.

The vulnerability allows a local or remote attacker who can cause the kernel to process files with crafted POSIX ACL entries to leak kernel memory repeatedly. This can lead to kernel memory exhaustion, potentially causing denial of service or system instability. There is no indication of privilege escalation or code execution from the provided data.

A fix is available and has been applied in the Linux kernel to free the leaked memory before breaking out of the loops. Users should update to the fixed kernel version containing this patch. Since this is not a cloud service, manual patching is required. Patch status is not explicitly confirmed in the input data, so check the vendor advisory for the exact fixed kernel versions and apply updates accordingly.