CVE-2026-31709
Description
A flaw was found in the Linux kernel's Server Message Block (SMB) client, specifically within the cifsacl functionality. A malicious SMB server could provide a malformed Discretionary Access Control List (DACL) that claims to contain more Access Control Entries (ACEs) than are actually present. This insufficient validation allows the kernel to read or copy data beyond the intended memory boundaries, leading to memory corruption. This could potentially result in information disclosure or a denial of service.
Mitigation
To mitigate this issue, if SMB client functionality is not required, the `cifs` kernel module can be blacklisted to prevent it from loading. This can be achieved by creating a modprobe configuration file.
1. Create a file named `/etc/modprobe.d/disable-cifs.conf` with the following content:
install cifs /bin/true2. Regenerate the initramfs to ensure the change takes effect on boot:
blacklist cifs
bashor for systems using `mkinitrd`:
dracut -f -v
bash3. A system reboot is required for the changes to take effect.
mkinitrd -f /boot/initramfs-$(uname -r).img $(uname -r)
Warning: Disabling the `cifs` module will prevent the system from mounting SMB/CIFS shares. Ensure this functionality is not critical before applying this mitigation.
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.8 | N/A | 7.8 |
| Attack Vector | Local | N/A | Local |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | Low | N/A | Low |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Other
Technical Impact: Varies by Context
Frequently Asked Questions
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