CVE-2026-98044: Linux Vulnerability

Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Reject legacy packet loads from callbacks check_ld_abs() models a failed BPF_LD_ABS or BPF_LD_IND in a subprogram as an implicit return with R0 set to zero. It calls prepare_func_exit() to explore this synthesized path. When the load is reached directly from a synchronous callback, prepare_func_exit() enforces the callback return contract and marks R0 precise. R0 is not derived from a real instruction on this path, so precision backtracking reaches the callback call with R0 still requested and triggers the "callback unexpected regs" verifier bug. A privileged program loader can therefore cause a verifier warning and an -EFAULT BPF_PROG_LOAD. These legacy packet-load instructions are deprecated. Reject them from callbacks rather than complicating their implicit-return model. Check all active frames before constructing the implicit return so nested static subprograms cannot hide the callback context. Global functions are verified independently with a fresh frame zero, so an active-frame check cannot identify a global function called from a callback. Also check the complete subprogram call graph during stack-depth validation and reject a function containing a legacy load when any caller is a callback. This covers global and static descendants without making has_ld_abs transitive, preserving its per-function BTF return-type check. Ordinary uses outside callbacks remain supported.

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= ce01a4e5cfac7adbe0be565f90cd32ecbb2f8337, < 3484a99303912db62428494a9061212049027e57; >= ee861486e377edc55361c08dcbceab3f6b6577bd, < bc489c0c9b8c86bd7fac42cfd1bb152f042fca56; >= ee861486e377edc55361c08dcbceab3f6b6577bd, < e7d28823c662128caae63f14e16bd394916c139b; 928d354ae3557e8f755a227e67be88034eb3cd7f; 8a800497d9f6c2ec9c2c1ba7b71d0ac2ea7f7bbe; de1055e7f9e67af32b1f3376066272b04e5223c0; 37ad2bb11e9de92cb7b94548705eeedd87f7d392; 8674e2db06cff6b50f2216eed9a761d15425bb34; d846d83bdacbd8f14fc45c63b8c1d22608452e1c; >= 6.18.42, < 6.18.53; >= 5.10.265, < 5.11; >= 5.15.216, < 5.16; >= 6.1.183, < 6.2; >= 6.6.148, < 6.7; >= 6.12.101, < 6.13; >= 7.0.10, < 7.1
Linux	Linux	7.1

References

Timeline

Published: Sep 25, 2026
Last Modified: Sep 25, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-98044?

In the Linux kernel, the following vulnerability has been resolved: bpf: Reject legacy packet loads from callbacks check_ld_abs() models a failed BPF_LD_ABS or BPF_LD_IND in a subprogram as an implicit return with R0 set to zero. It calls prepare_func_exit() to explore this synthesized path. When the load is reached directly from a synchronous callback, prepare_func_exit() enforces the callback return contract and marks R0 precise. R0 is not derived from a real instruction on this path, so precision backtracking reaches the callback call with R0 still requested and triggers the "callback unexpected regs" verifier bug. A privileged program loader can therefore cause a verifier warning and an -EFAULT BPF_PROG_LOAD. These legacy packet-load instructions are deprecated. Reject them from callbacks rather than complicating their implicit-return model. Check all active frames before constructing the implicit return so nested static subprograms cannot hide the callback context. Global functions are verified independently with a fresh frame zero, so an active-frame check cannot identify a global function called from a callback. Also check the complete subprogram call graph during stack-depth validation and reject a function containing a legacy load when any caller is a callback. This covers global and static descendants without making has_ld_abs transitive, preserving its per-function BTF return-type check. Ordinary uses outside callbacks remain supported.

How severe is CVE-2026-98044?

Severity scoring for CVE-2026-98044 is pending analysis.

How do I fix CVE-2026-98044?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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