Linux Kernel BPF check_helper_call input validation

Summaryinfo

A vulnerability categorized as very critical has been discovered in Linux Kernel. Affected is the function check_helper_call of the component BPF. Such manipulation leads to input validation. This vulnerability is uniquely identified as CVE-2026-98084. Local access is required to approach this attack. No exploit exists. It is best practice to apply a patch to resolve this issue.

Detailsinfo

A vulnerability, which was classified as very critical, has been found in Linux Kernel (affected version unknown). Affected by this issue is the function check_helper_call of the component BPF. The manipulation with an unknown input leads to a input validation vulnerability. Using CWE to declare the problem leads to CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Impacted is confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: bpf: backtracking shouldn't clear outer frame R1-R5 for callbacks When processing calls to bpf_loop() verifier marks R1 (and R4) as precise. R1 tracks loop iterations number and because of the 'callback_depth < R1' mechanics in check_helper_call() must be marked precise. However, precision propagation for R1 was broken, when bpf_loop() call was verified on a second iteration. Consider the following verification trace: - main: bpf_loop(nr_loops, callback ...) - callback: BPF_EXIT - main: bpf_loop(nr_loops, callback ...) - ... While the first visit of the call to bpf_loop() propagated R1 precision as expected, the second call to mark_chain_precision() in the check_helper_call() set R1, but it was immediately reset when backtrack_insn() processed preceding BPF_EXIT in the loop deleted in this patch. Because of that, the second visit of the call to bpf_loop() injected checkpoint with R1 not marked as precise. Which could trick the verifier into accepting unsafe programs. See the next patch for an example of such program. Commit is structured in a way to minimize conflicts when 'bpf' would be eventually merged with 'bpf-next'.

The advisory is available at git.kernel.org. This vulnerability is handled as CVE-2026-98084 since 09/25/2026. The exploitation is known to be easy. Local access is required to approach this attack. Additional levels of successful authentication are required for exploitation. 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 09/25/2026).

Applying the patch f83890dfed9efc5e19df1dbc1ad707a142936923/e3e4f66cc4b72333d0886ae2673c360248987889 is able to eliminate this problem.

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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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