Linux Kernel Cmis cmis_cdb_process_reply rpl_len/rpl_exp_len out-of-bounds write

Summaryinfo

A vulnerability identified as very critical has been detected in Linux Kernel. The affected element is the function cmis_cdb_process_reply of the component Cmis. Performing a manipulation of the argument rpl_len/rpl_exp_len results in out-of-bounds write. This vulnerability is cataloged as CVE-2026-63996. The attack must be initiated from a local position. There is no exploit available.

Detailsinfo

A vulnerability classified as very critical has been found in Linux Kernel (affected version not known). This affects the function cmis_cdb_process_reply of the component Cmis. The manipulation of the argument rpl_len/rpl_exp_len with an unknown input leads to a out-of-bounds write vulnerability. CWE is classifying the issue as CWE-787. The product writes data past the end, or before the beginning, of the intended buffer. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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) comes from last arg to ethtool_cmis_page_init() which is rpl_exp_len. Note2 that AIs also like to point out overflows in args->req.payload itself (which is a fixed-size 120 B buffer, on the stack), but callers should be reading structs defined by the standard, so protecting from requests for more data than max seem like defensive programming.

This vulnerability is uniquely identified as CVE-2026-63996. The exploitability is told to be easy. An attack has to be approached locally. Technical details are known, but no exploit is available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 10/04/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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