CVE-2026-99272
Description
A flaw was found in the Linux kernel's Server Message Block (SMB) client. The SMB2 read handler does not properly validate whether the data range specified by the server fits within the boundaries of the received packet. A malicious SMB server could exploit this vulnerability by sending a crafted read response with an invalid data offset and length, triggering an out-of-bounds memory read. This issue can lead to a system crash, resulting in a Denial of Service (DoS), or potentially expose sensitive kernel memory.
Statement
This vulnerability is rated as Important because a rogue or compromised SMB server can induce a kernel-space slab out-of-bounds read, leading directly to a client system crash or potential memory disclosure. Exploitation depends on a user or automated process initiating file operations against an untrusted network share, limiting the attack surface to active CIFS client connections. Red Hat Enterprise Linux systems that do not mount remote SMB shares or that restrict mounts to trusted internal infrastructure are not vulnerable to external exploitation.
Mitigation
To mitigate this vulnerability, prevent the cifs kernel module from loading if SMB client mounts are not required:
1. Create a configuration file to prevent the module from being loaded:
echo "install cifs /bin/true" > /etc/modprobe.d/disable-cifs.conf
2. If the module is currently loaded, unmount all active CIFS shares and attempt to remove it:
modprobe -r cifs
Warning: Unloading the kernel module will terminate active SMB connections, and a system reboot may be required to fully ensure the module remains unloaded if it is currently held in use by running processes.
Caveats:
Disabling the cifs module prevents the system from mounting remote SMB/CIFS file shares. If SMB client functionality is business-critical, ensure mounts are strictly restricted to trusted internal SMB servers.
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 | 7.1 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | Required | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | Low | 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:N/UI:R/S:U/C:L/I:N/A:H
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
An attacker could get secret values such as cryptographic keys, PII, memory addresses, or other information that could be used in additional attacks.
Confidentiality
Technical Impact: Bypass Protection Mechanism
Out-of-bounds memory could contain memory addresses or other information that can be used to bypass ASLR and other protection mechanisms in order to improve the reliability of exploiting a separate weakness for code execution.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
An attacker could cause a segmentation fault or crash by causing memory to be read outside of the bounds of the buffer. This is especially likely when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string.
Other
Technical Impact: Varies by Context
The read operation could produce other undefined or unexpected results.
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