CVE-2025-39928
📋 TL;DR
A vulnerability in the Linux kernel's i2c driver for Realtek RTL9300 chips allows improper handling of zero-length data transfers. This can cause unintended 16-byte write operations instead of SMBus Quick Operations, potentially damaging hardware like SFP modules. Systems using affected Realtek hardware with vulnerable kernel versions are at risk.
💻 Affected Systems
- Linux kernel with Realtek RTL9300 i2c driver
📦 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 →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
Permanent hardware damage (soft-bricking) of connected devices like SFP modules by overwriting critical EEPROM data, requiring hardware replacement.
Likely Case
Data corruption or device malfunction when SMBus Quick Operations are attempted on vulnerable hardware, potentially disrupting network equipment functionality.
If Mitigated
No impact if patched kernel is used or if vulnerable hardware isn't present in the system.
🎯 Exploit Status
Exploitation requires triggering zero-length SMBus operations on vulnerable hardware, which may require specific hardware access or privileged software execution.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel versions containing commits 06418cb5a1a542a003fdb4ad8e76ea542d57cfba and c91382328fc89f73144d5582f2d8f1dd3e41c8f7
Vendor Advisory: https://git.kernel.org/stable/c/06418cb5a1a542a003fdb4ad8e76ea542d57cfba
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix commits. 2. Check kernel source for commits 06418cb5a1a542a003fdb4ad8e76ea542d57cfba and c91382328fc89f73144d5582f2d8f1dd3e41c8f7. 3. Reboot system after kernel update.
🔧 Temporary Workarounds
Disable vulnerable i2c driver
linuxBlacklist or disable the rtl9300 i2c driver module to prevent loading
echo 'blacklist i2c-rtl9300' >> /etc/modprobe.d/blacklist.conf
rmmod i2c-rtl9300
Restrict i2c device access
linuxLimit access to i2c devices using permissions or access controls
chmod 600 /dev/i2c-*
setfacl -m u:root:rw /dev/i2c-*
🧯 If You Can't Patch
- Isolate systems with vulnerable hardware from untrusted users and applications
- Monitor for SMBus Quick Operations on affected hardware and alert on suspicious activity
🔍 How to Verify
Check if Vulnerable:
Check if kernel contains vulnerable driver: lsmod | grep i2c_rtl9300 && uname -r | compare with patched versionsCheck Version:
uname -rVerify Fix Applied:
Verify kernel version contains fix commits: git log --oneline | grep -E '06418cb5a1a542a003fdb4ad8e76ea542d57cfba|c91382328fc89f73144d5582f2d8f1dd3e41c8f7'📡 Detection & Monitoring
Log Indicators:
- Kernel logs showing i2c errors or SMBus operation failures
- Hardware error messages related to EEPROM writes
Network Indicators:
- Unusual i2c traffic patterns or failed device communications
SIEM Query:
source="kernel" AND ("i2c" OR "SMBus") AND ("error" OR "failure" OR "rtl9300")