Linux Kernel up to 6.16.7 SFP Module rtl9300_i2c_config_xfer missing initialization

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.16.7 and classified as critical. The impacted element is the function rtl9300_i2c_config_xfer of the component SFP Module. Such manipulation leads to missing initialization. This vulnerability is listed as CVE-2025-39928. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.16.7 and classified as critical. Affected by this issue is the function rtl9300_i2c_config_xfer of the component SFP Module. The manipulation with an unknown input leads to a missing initialization vulnerability. Using CWE to declare the problem leads to CWE-456. The product does not initialize critical variables, which causes the execution environment to use unexpected values. The impact remains unknown. CVE summarizes:

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

The advisory is available at git.kernel.org. This vulnerability is handled as CVE-2025-39928 since 04/16/2025. The exploitation is known to be difficult. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 01/08/2026).

The vulnerability scanner Nessus provides a plugin with the ID 269663 (Linux Distros Unpatched Vulnerability : CVE-2025-39928), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.16.8 eliminates this vulnerability. Applying the patch c91382328fc89f73144d5582f2d8f1dd3e41c8f7/06418cb5a1a542a003fdb4ad8e76ea542d57cfba is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (269663), EUVD (EUVD-2025-31823) and CERT Bund (WID-SEC-2025-2170). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Affected

• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• RESF Rocky Linux
• Open Source Linux Kernel
• Dell Secure Connect Gateway

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.16.0
• 6.16.1
• 6.16.2
• 6.16.3
• 6.16.4
• 6.16.5
• 6.16.6
• 6.16.7

License

• open-source

Website

• Vendor: https://www.kernel.org/

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If you want to get best quality of vulnerability data, you may have to visit VulDB.

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