# CVE-2025-39928: linux: In the Linux kernel, the following vulnerability has been resolved:  i2c: rtl9300: ensure data length is within suppo...

CVE-2025-39928 is fixed in linux on 1 platform by DEBIAN-CVE-2025-39928 (version 6.16.8-1), released October 1, 2025. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2025-39928
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0013
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 1, 2025

## 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

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 6.16.8-1 | [DEBIAN-CVE-2025-39928](https://patchblox.com/security/data/fix/linux/debian-cve-2025-39928.md) | Oct 1, 2025 |

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