CVE-2026-99275
Description
A flaw was found in the Linux kernel's SMB (Server Message Block) client. A malicious SMB server can exploit this vulnerability to trigger an out-of-bounds memory read, leading to sensitive information disclosure. Due to missing packet length checks on truncated session setup responses, the client reads unvalidated buffer metadata and copies adjacent kernel memory into outgoing authentication traffic sent back to the server.
Statement
This vulnerability is rated as Moderate severity because exploitation requires an affected client system to actively initiate a connection to a rogue or compromised SMB server. Under typical Red Hat Enterprise Linux deployments, the kernel CIFS client is not exposed to unsolicited inbound network traffic and only executes when explicitly mounting remote shares. While an attacker operating a malicious SMB server can trigger an out-of-bounds memory read and obtain up to 64 KB of kernel memory via crafted session setup responses during authentication, the flaw does not allow remote code execution or modification of system data.
Mitigation
To mitigate this vulnerability on systems where mounting remote SMB/CIFS file shares is not required, prevent the CIFS kernel module from loading:
1. Create a configuration file in `/etc/modprobe.d/` to disable autoloading:
echo "install cifs /bin/true" > /etc/modprobe.d/disable-cifs.conf
2. If the module is currently loaded, ensure all active CIFS shares are unmounted before unloading the module:
modprobe -r cifs
Caveats:
Disabling or unloading the `cifs` module prevents the system from mounting SMB/CIFS network shares. Unmounting active shares may disrupt applications or users accessing files on those mounts. On systems where SMB client functionality is mandatory, ensure connections are strictly restricted to trusted file 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 | 6.5 | 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 | High | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | None | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
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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