CVE-2025-39928

Full vulnerability record from the local CVENow database.

Description

In the Linux kernel, the following vulnerability has been resolved: i2c: rtl9300: ensure data length is within supported range Add an explicit check for the xfer length to 'rtl9300_i2c_config_xfer' to ensure the data length isn't within the supported range. In particular a data length of 0 is not supported by the hardware and causes unintended or destructive behaviour. This limitation becomes obvious when looking at the register documentation [1]. 4 bits are reserved for DATA_WIDTH and the value of these 4 bits is used as N + 1, allowing a data length range of 1 <= len <= 16. Affected by this is the SMBus Quick Operation which works with a data length of 0. Passing 0 as the length causes an underflow of the value due to: (len - 1) & 0xf and effectively specifying a transfer length of 16 via the registers. This causes a 16-byte write operation instead of a Quick Write. For example, on SFP modules without write-protected EEPROM this soft-bricks them by overwriting some initial bytes. For completeness, also add a quirk for the zero length. [1] https://svanheule.net/realtek/longan/register/i2c_mst1_ctrl2

Severity

MEDIUM

CVSS score

5.5 (v3.1)

Vulnerability status

Modified

Source identifier

416baaa9-dc9f-4396-8d5f-8c081fb06d67

Published

2025-10-01 08:15:36.230000

Last modified

2026-10-19 21:10:00.160000

View original CVE JSON

{
  "id": "CVE-2025-39928",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2025-10-01T08:15:36.230",
  "lastModified": "2026-10-19T21:10:00.160",
  "vulnStatus": "Modified",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ni2c: rtl9300: ensure data length is within supported range\n\nAdd an explicit check for the xfer length to 'rtl9300_i2c_config_xfer'\nto ensure the data length isn't within the supported range. In\nparticular a data length of 0 is not supported by the hardware and\ncauses unintended or destructive behaviour.\n\nThis limitation becomes obvious when looking at the register\ndocumentation [1]. 4 bits are reserved for DATA_WIDTH and the value\nof these 4 bits is used as N + 1, allowing a data length range of\n1 <= len <= 16.\n\nAffected by this is the SMBus Quick Operation which works with a data\nlength of 0. Passing 0 as the length causes an underflow of the value\ndue to:\n\n(len - 1) & 0xf\n\nand effectively specifying a transfer length of 16 via the registers.\nThis causes a 16-byte write operation instead of a Quick Write. For\nexample, on SFP modules without write-protected EEPROM this soft-bricks\nthem by overwriting some initial bytes.\n\nFor completeness, also add a quirk for the zero length.\n\n[1] https://svanheule.net/realtek/longan/register/i2c_mst1_ctrl2"
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\ni2c: rtl9300: asegurar que la longitud de los datos esté dentro del rango soportado\n\nAñadir una verificación explícita para la longitud de la transferencia a 'rtl9300_i2c_config_xfer' para asegurar que la longitud de los datos esté dentro del rango soportado. En particular, una longitud de datos de 0 no es soportada por el hardware y causa un comportamiento no deseado o destructivo.\n\nEsta limitación se hace obvia al observar la documentación del registro [1]. 4 bits están reservados para DATA_WIDTH y el valor de estos 4 bits se usa como N + 1, permitiendo un rango de longitud de datos de 1 <= len menor o igual que 16.\n\nAfectada por esto es la Operación Rápida SMBus que funciona con una longitud de datos de 0. Pasar 0 como longitud causa un desbordamiento negativo del valor debido a:\n\n(len - 1) & 0xf\n\ny especificando efectivamente una longitud de transferencia de 16 a través de los registros. Esto causa una operación de escritura de 16 bytes en lugar de una Escritura Rápida. Por ejemplo, en módulos SFP sin EEPROM protegida contra escritura, esto los inutiliza parcialmente al sobrescribir algunos bytes iniciales.\n\nPara completar, añadir también una peculiaridad para la longitud cero.\n\n[1] HTTPS://svanheule.net/realtek/longan/register/i2c_mst1_ctrl2"
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