CVE-2026-31693: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-31693 is a missing/uninitialized variable vulnerability in the Linux kernel's CIFS (Common Internet File System) subsystem, specifically in the request replay code paths. In several locations, replay labels that mark the start of retryable CIFS request handling were missing necessary reinitializations of local variables, causing those variables to be used in an uninitialized state during replayed operations. The vulnerability affects Linux kernel versions from 6.6.32 through 6.6.127, 6.8 through 6.12.74, 6.13 through 6.18.15, and 6.19 through 6.19.5. It was published on April 30, 2026, with a CVSS v3.1 base score of 7.8 (High) (GitHub Advisory, Red Hat).

The root cause is classified under CWE-909 (Missing Initialization of Resource) and CWE-908 (Use of Uninitialized Resource). In the Linux kernel CIFS subsystem, certain code paths use a goto label to replay SMB requests when necessary (e.g., after session reconnection). However, several of these replay labels were missing reinitializations of local variables that had been set earlier in the function, meaning that on a replay iteration, those variables would retain stale or garbage values. An attacker with local access and low privileges who can trigger CIFS operations — such as by mounting a CIFS share — could cause these uninitialized variables to be consumed by kernel logic, potentially leading to memory corruption or information leakage (GitHub Advisory, Red Hat).

A local user with low privileges can exploit this vulnerability to potentially achieve information disclosure (reading kernel memory contents via uninitialized variables), data corruption of CIFS-related operations, or privilege escalation through kernel memory manipulation. The vulnerability is confined to systems actively using CIFS mounts; systems that do not use CIFS are not affected. The CVSS v3.1 scoring reflects high impacts to confidentiality, integrity, and availability within the unchanged scope of the affected system (GitHub Advisory, Red Hat).

There is no public proof-of-concept exploit and no evidence of in-the-wild exploitation as of the time of publication (GitHub Advisory). The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is approximately 0.018% (0.000180), indicating a very low probability of exploitation in the near term. Exploitation requires local access with low privileges and the ability to trigger CIFS replay operations, limiting the practical attack surface.

Update the Linux kernel to a patched version: 6.6.128 or later, 6.12.75 or later, 6.18.16 or later, 6.19.6 or later, or 7.0 and later. Patches are available in the kernel stable git repository via commits c854ab48, 1d731e51, 7c9ce681, c99e1609, and 14f66f44. If immediate patching is not possible, restrict CIFS mount access to trusted users only and monitor for unusual CIFS-related kernel behavior. Systems not using CIFS mounts are not affected by this vulnerability (GitHub Advisory, Red Hat, Amazon Linux).

Red Hat has acknowledged the vulnerability and assigned it a Bugzilla entry, rating it as moderate severity (Red Hat). Amazon Linux has issued a security advisory (ALAS2023-2026-1702) addressing this CVE (Amazon Linux). Oracle Linux has also addressed the issue as part of UEK kernel updates (Linux Compatible). No significant social media discussion or notable researcher commentary has been observed beyond standard vulnerability tracking.