Linux Kernel up to 7.2.6/7.3-rc1 BPF states.c __clean_func_state downgrade

Summaryinfo

A vulnerability marked as critical has been reported in Linux Kernel up to 7.2.6/7.3-rc1. Affected by this vulnerability is the function __clean_func_state of the file states.c of the component BPF. Performing a manipulation results in downgrade. This vulnerability is cataloged as CVE-2026-98132. The attack must be initiated from a local position. There is no exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical has been found in Linux Kernel up to 7.2.6/7.3-rc1. This affects the function __clean_func_state of the file states.c of the component BPF. The manipulation with an unknown input leads to a downgrade vulnerability. CWE is classifying the issue as CWE-757. A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used as a protection mechanism such as encryption or authentication, but it does not select the strongest algorithm that is available to both parties. 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: bpf: don't downgrade half-dead scalar zero spills to STACK_ZERO states.c:__clean_func_state() can downgrade scalar zero spill to STACK_ZERO in the following case: *(u64 *)(r10 - 8) = 0; ... checkpoint ... r1 = *(u32 *)(r10 - 4); ... no reads from r10-8 ... Here 4 bytes at r10-8 are dead and verifier changes scalar spill to a combination: 0000pppp (p stands for poison). Such a change breaks precision propagation chains. All places that produce STACK_ZERO should call bpf_mark_chain_precision() for the zero source. This patch fixes the bug in a simplest way possible: avoids converting stack spills of zero to STACK_ZERO. Two smarter approaches are possible: - do bpf_mark_chain_precision() from __clean_func_state() - check slot liveness information in check_stack_write_fixed_off() I investigated both and the changes required are a bit tricky, hence go with a simple fix for the time being.

It is possible to read the advisory at git.kernel.org. This vulnerability is uniquely identified as CVE-2026-98132 since 09/25/2026. The exploitability is told to be easy. Attacking locally is a requirement. Additional levels of successful authentication are needed for exploitation. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1562.010 according to MITRE ATT&CK.

Upgrading to version 7.2.7 or 7.3-rc2 eliminates this vulnerability. Applying the patch 436fa689630b741a77ef8c4a6f426479affd5bac/2f3536bff8823d3c5fdbbe15e17bfca696cc2b2e is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.2.6
• 7.3-rc1

License

• open-source

Website

• Vendor: https://www.kernel.org/

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