CVE-2025-38685 – This vulnerability in the Linux kernel's fbdev ... (How to Fix)

Q: What is the severity of CVE-2025-38685?

CVE-2025-38685 has a CVSS score of 7.8 (HIGH). This vulnerability in the Linux kernel's fbdev subsystem allows a local user to trigger an out-of-bounds write in the fast_imageblit function when performing console-to-framebuffer mapping operations. The flaw occurs when console resize fails but the system continues with inconsistent data structures, leading to memory corruption. This affects Linux systems with framebuffer console support enabled.

📋 TL;DR

This vulnerability in the Linux kernel's fbdev subsystem allows a local user to trigger an out-of-bounds write in the fast_imageblit function when performing console-to-framebuffer mapping operations. The flaw occurs when console resize fails but the system continues with inconsistent data structures, leading to memory corruption. This affects Linux systems with framebuffer console support enabled.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not specified in CVE, but patches exist in stable kernel trees

Operating Systems: Linux distributions with vulnerable kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Requires framebuffer console support (CONFIG_FRAMEBUFFER_CONSOLE) and users with access to FBIOPUT_CON2FBMAP ioctl. Most desktop/server Linux systems are potentially affected.

📦 What is this software?

Debian Linux by Debian

View all CVEs affecting Debian Linux →

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...

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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 →

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 →

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

Local privilege escalation to kernel-level code execution, potentially leading to full system compromise, data theft, or persistent backdoor installation.

🟠

Likely Case

Kernel panic or system crash causing denial of service, with potential for limited privilege escalation in carefully crafted attacks.

🟢

If Mitigated

System remains stable with no impact if the vulnerable code path isn't triggered or if proper access controls prevent unauthorized users from performing FBIOPUT_CON2FBMAP operations.

🌐 Internet-Facing: LOW - This requires local access to trigger the vulnerable ioctl operation.

🏢 Internal Only: MEDIUM - Local users or compromised accounts could exploit this, but requires specific console/framebuffer operations.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires local access and ability to perform specific framebuffer console operations. Exploit would need to trigger the resize failure path and subsequent inconsistent state.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Patched in stable kernel versions via commits referenced in CVE

Vendor Advisory: https://git.kernel.org/stable/c/078e62bffca4b7e72e8f3550eb063ab981c36c7a

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution's repositories. 2. For custom kernels, apply patches from stable kernel git tree. 3. Reboot system to load new kernel.

🔧 Temporary Workarounds

Disable framebuffer console

linux

Remove framebuffer console support to eliminate vulnerable code path

Remove CONFIG_FRAMEBUFFER_CONSOLE from kernel configuration and rebuild kernel

Restrict console device access

linux

Limit access to console devices to prevent unauthorized FBIOPUT_CON2FBMAP operations

chmod 600 /dev/tty*
setfacl -m u:root:rw /dev/tty*

🧯 If You Can't Patch

Restrict local user access to systems with vulnerable kernels
Implement strict access controls on console and framebuffer devices

🔍 How to Verify

Check if Vulnerable:

Check kernel version and if framebuffer console is enabled: cat /proc/config.gz | gunzip | grep CONFIG_FRAMEBUFFER_CONSOLE

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version is updated to include the fix commits: uname -r and check with distribution vendor

📡 Detection & Monitoring

Log Indicators:

Kernel oops messages
System crashes related to fbcon_putcs or fast_imageblit
Unexpected console/framebuffer mapping operations

Network Indicators:

None - local exploit only

SIEM Query:

source="kernel" AND ("fbcon_putcs" OR "fast_imageblit" OR "FBIOPUT_CON2FBMAP")

📊 Metadata

CVE ID: CVE-2025-38685

CVSS v3 Score: 7.8 (HIGH)

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

CWE: CWE-787

EPSS Score: 0.02% exploit probability (4.1th percentile)

Published: September 4, 2025

Last Updated: January 8, 2026

🔗 References

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