CVE-2026-99277
Description
A flaw was found in the Linux kernel's ksmbd, an in-kernel Server Message Block (SMB) server. A remote attacker could exploit this flaw to cause a denial of service (DoS) or potentially corrupt kernel memory. The issue occurs due to improper reference counting during session channel management, where a connection structure can be freed while still in use by an active session channel. By triggering concurrent SMB operations, an attacker can induce a use-after-free condition leading to a system crash.
Statement
This vulnerability is rated as Moderate because successful exploitation requires authenticated network access to establish SMB session channels and primarily leads to a denial of service via a kernel crash. In Red Hat Enterprise Linux, the in-kernel SMB server (ksmbd) is not loaded or configured by default, as standard installations rely on user-space Samba for SMB file sharing. Only systems where administrators have explicitly enabled and deployed ksmbd are exposed to this flaw.
Mitigation
Disable the ksmbd kernel module to prevent it from loading:
1. Create a configuration file in /etc/modprobe.d to disable module loading:
echo "install ksmbd /bin/true" > /etc/modprobe.d/ksmbd.conf
2. If the module is currently loaded, unload it:
modprobe -r ksmbd
Caveats:
Disabling the ksmbd module prevents the system from running the in-kernel SMB server. If the module is actively in use by SMB sessions, dependent services must be stopped prior to unloading, or a system restart may be required to apply the changes.
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 | 6.5 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | Low | 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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
If the expired pointer is used in a read operation, an attacker might be able to control data read in by the application.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If the expired pointer references a memory location that is not accessible to the product, or points to a location that is "malformed" (such as NULL) or larger than expected by a read or write operation, then a crash may occur.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If the expired pointer is used in a function call, or points to unexpected data in a write operation, then code execution may be possible.
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