CVE-2025-21748 – This CVE describes an integer overflow vulnerab... (How to Fix)

Q: What is the severity of CVE-2025-21748?

CVE-2025-21748 has a CVSS score of 5.5 (MEDIUM). This CVE describes an integer overflow vulnerability in the ksmbd (kernel SMB server) module of the Linux kernel on 32-bit systems. The overflow occurs during memory allocation operations, potentially leading to memory corruption. Systems running 32-bit Linux kernels with ksmbd enabled are affected.

📋 TL;DR

This CVE describes an integer overflow vulnerability in the ksmbd (kernel SMB server) module of the Linux kernel on 32-bit systems. The overflow occurs during memory allocation operations, potentially leading to memory corruption. Systems running 32-bit Linux kernels with ksmbd enabled are affected.

💻 Affected Systems

Products:

Linux kernel with ksmbd module

Versions: Linux kernel versions before the fix commits (specific versions vary by distribution)

Operating Systems: Linux distributions running 32-bit kernels

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when ksmbd module is loaded and active. Most modern systems use 64-bit kernels, limiting exposure.

📦 What is this software?

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Successful exploitation could lead to kernel memory corruption, potentially resulting in system crashes, privilege escalation, or arbitrary code execution in kernel context.

🟠

Likely Case

Most probable impact is system instability, kernel panics, or denial of service through memory corruption leading to crashes.

🟢

If Mitigated

With proper kernel hardening and ksmbd disabled or restricted, impact is limited to denial of service at worst.

🌐 Internet-Facing: MEDIUM - ksmbd is typically used for file sharing services which may be exposed to internal networks rather than directly internet-facing, but SMB services exposed to untrusted networks increase risk.

🏢 Internal Only: MEDIUM - Internal systems with ksmbd enabled on 32-bit kernels are vulnerable to memory corruption attacks from authenticated users.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires triggering the specific integer overflow condition in ipc_msg_alloc() function, likely requiring authenticated access to ksmbd services.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing the fix commits: 760568c1f62e, 82f59d64e629, aab98e2dbd64, b4b902737746, ecb9947fa7c9

Vendor Advisory: https://git.kernel.org/stable/c/760568c1f62ea874e8fb492f9cfa4f47b4b8391e

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing the fix commits. 2. Reboot system to load new kernel. 3. Verify ksmbd module is using patched version.

🔧 Temporary Workarounds

Disable ksmbd module

linux

Unload the ksmbd kernel module if not required

sudo rmmod ksmbd
echo 'blacklist ksmbd' | sudo tee /etc/modprobe.d/blacklist-ksmbd.conf

Restrict ksmbd access

linux

Limit ksmbd service to trusted networks only

sudo firewall-cmd --permanent --zone=trusted --add-service=samba
sudo firewall-cmd --reload

🧯 If You Can't Patch

Disable ksmbd service completely if not required
Migrate affected systems to 64-bit kernel architecture

🔍 How to Verify

Check if Vulnerable:

Check if running 32-bit kernel with ksmbd module loaded: 'uname -m' should show i686 or i386, and 'lsmod | grep ksmbd' should show module loaded.

Check Version:

uname -r

Verify Fix Applied:

Check kernel version contains fix commits: 'uname -r' and verify with distribution's security advisory. Check ksmbd module version if possible.

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages
OOM (Out of Memory) errors in dmesg
ksmbd service crashes

Network Indicators:

Unusual SMB traffic patterns to ksmbd services
Multiple connection attempts to ksmbd

SIEM Query:

source="kernel" AND ("panic" OR "Oops" OR "BUG") AND process="ksmbd"

📊 Metadata

CVE ID: CVE-2025-21748

CVSS v3 Score: 5.5 (MEDIUM)

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-190

EPSS Score: 0.05% exploit probability (16.5th percentile)

Published: February 27, 2025

Last Updated: November 3, 2025

🔗 References

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