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How the Mentioned CVE Works
The vulnerability exists in the `rtl9300_i2c_config_xfer` function within the Linux kernel’s I2C driver for Realtek RTL9300 switch SoCs. The hardware’s I2C controller register (I2C_MST1_CTRL2) uses a 4-bit `DATA_WIDTH` field to set transfer length, where the configured value equals N+1 bytes. This design only supports a data length range of 1 to 16 bytes. The driver failed to validate the input length before programming this register. When an SMBus “Quick Command” with a data length of 0 is processed, the calculation `(len – 1) & 0xf` causes an integer underflow, resulting in a `DATA_WIDTH` value of 16 (0xf + 1). Consequently, the hardware performs an unintended 16-byte write operation instead of a single-byte Quick Write. On susceptible systems, such as those managing SFP modules, this can overwrite critical bytes in a device’s EEPROM, potentially causing a permanent soft-brick.
DailyCVE Form
Platform: Linux Kernel
Version: i2c-rtl9300 driver
Vulnerability: Out-of-bounds write
Severity: Critical
date: 10/01/2025
Prediction: 2025-10-08
What Undercode Say
Analytics
Check if the vulnerable i2c module is loaded lsmod | grep i2c_rtl9300 Extract kernel version uname -r Query specific kernel config (if available) zcat /proc/config.gz | grep I2C_RTL9300
Code Snippet (Vulnerable Logic):
// In drivers/i2c/busses/i2c-rtl9300.c
static int rtl9300_i2c_config_xfer(... u8 len ...) {
// MISSING VALIDATION: if (len == 0 || len > 16) return -EINVAL;
u32 val = (len - 1) & 0xf; // UNDERFLOW WHEN len=0
rtl9300_i2c_writel(i2c, I2C_MST1_CTRL2, ... | (val << 4));
}
Code Snippet (Patch Applied):
// Patch adds explicit length check
static int rtl9300_i2c_config_xfer(... u8 len ...) {
if (len == 0 || len > 16) // Explicit validation
return -EINVAL;
u32 val = (len - 1) & 0xf;
rtl9300_i2c_writel(i2c, I2C_MST1_CTRL2, ... | (val << 4));
}
How Exploit
An attacker with local or remote (depending on I2C accessibility) capability can issue an SMBus Quick Write command (data length 0) to a system using the vulnerable `i2c-rtl9300` driver. This triggers the register miscalculation, forcing a 16-byte write starting at the target device’s current address pointer. For example, targeting an SFP module’s EEPROM at address 0x50 would overwrite its first 16 bytes (often containing vital identification and calibration data), rendering the hardware inoperable.
Protection from this CVE
Apply the official kernel patch that adds the length check in rtl9300_i2c_config_xfer. Update the entire Linux kernel to a version containing the fix. As an interim mitigation, restrict access to I2C/SMBus interfaces or unload the `i2c_rtl9300` module if not required (rmmod i2c_rtl9300).
Impact
The primary impact is the irreversible corruption of connected I2C device memory, such as SFP/QSFP module EEPROMs, leading to bricked hardware. Systems using Realtek RTL9300-based switches for network hardware management are at direct risk. The vulnerability compromises hardware integrity and availability, requiring physical replacement of affected components.
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Sources:
Reported By: nvd.nist.gov
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