CVE-2026-63996

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

ethtool: cmis: require exact CDB reply length

Malicious SFP module could respond with rpl_len longer than

what cmis_cdb_process_reply() expected, leading to OOB writes.

Malicious HW is a bit theoretical but some modules may just

be buggy and/or the reads may occasionally get corrupted,

so let's protect the kernel.

The existing check protects from short replies. We need to

protect from long ones, too. All callers that pass a non-zero

rpl_exp_len cast the reply payload to a fixed-layout struct

and read fields at fixed offsets, with no version negotiation

or short-reply handling:

- cmis_cdb_validate_password()

- cmis_cdb_module_features_get()

- cmis_fw_update_fw_mng_features_get()

so let's assume that responses longer than expected do not

have to be handled gracefully here. Add a warning message

to make the debug easier in case my understanding is wrong...

Note that page_data->length (argument of kmalloc) come

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References