CVE-2026-99276
Description
A flaw was found in the Linux kernel's ksmbd (Server Message Block) server. A remote client can cause a Denial of Service (DoS) by triggering a deadlock condition during concurrent session teardown and connection cleanup operations. Because the periodic connection cleanup worker and session termination routines acquire internal locks in conflicting orders, simultaneous requests can become permanently blocked, causing the server to hang.
Statement
This vulnerability is assessed with a Moderate impact because a deadlock can trigger a denial of service without compromising system confidentiality or integrity. Exploitation requires specific race conditions between simultaneous session termination and connection scavenging on an actively serving kernel SMB instance. Red Hat Enterprise Linux relies on userspace Samba by default for SMB file sharing, meaning the in-kernel ksmbd server is not running or enabled on standard configurations.
Mitigation
If the in-kernel SMB server is not required, prevent the system from loading the ksmbd kernel module by adding a configuration rule:
# echo "install ksmbd /bin/true" > /etc/modprobe.d/ksmbd.conf
If the module is currently loaded, stop any active ksmbd services and unload the module:
# modprobe -r ksmbd
Warning: Unloading the kernel module or restricting service access will terminate active SMB sessions and prevent file sharing via ksmbd. If the module cannot be immediately unloaded because it is in use, a system reboot is required for the blacklist configuration to take effect. If ksmbd is required in your environment, restrict incoming network access to trusted hosts using firewall rules.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | High | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Other); DoS: Crash, Exit, or Restart
Each thread of execution will "hang" and prevent tasks from completing. In some cases, CPU consumption may occur if a lock check occurs in a tight loop.
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