The Linux kernel vulnerability CVE-2026-64598 involves an error in the SMB client code where the 'num_sgs' variable, a u32, was incorrectly handled as an error pointer, leading to potential kernel crashes. The fix involved storing the return value in an int variable to avoid invalid pointer dereferencing. This vulnerability was resolved in Linux kernel versions starting from 7.0.0-31.31 and related builds. The issue could cause system crashes impacting availability. The vendor advisory from Ubuntu confirms the availability of patches and recommends updating to specific fixed kernel package versions. The advisory also notes a broad set of other kernel security fixes in the same update cycle.

Exploitation of this vulnerability could cause a system crash due to dereferencing an invalid error pointer in the SMB client code, impacting system availability. The CVSS score of 8.8 reflects high impact on confidentiality, integrity, and availability, although no known exploits are reported in the wild. The flaw could lead to denial of service conditions on affected systems.

A patch is available and should be applied by updating to the fixed Linux kernel versions as specified in the Ubuntu security advisories USN-8726-1 and USN-8727-1. After updating, a system reboot is required to apply the changes. Due to an ABI change, recompilation and reinstallation of any third-party kernel modules are necessary. No additional mitigation steps are indicated by the vendor.