Linux Kernel up to 7.2.6/7.3-rc1 BPF check_cond_jmp_op null pointer dereference

Summaryinfo

A vulnerability classified as very critical has been found in Linux Kernel up to 7.2.6/7.3-rc1. Affected is the function check_cond_jmp_op of the component BPF. The manipulation leads to null pointer dereference. This vulnerability is referenced as CVE-2026-98040. Remote exploitation of the attack is possible. No exploit is available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.2.6/7.3-rc1. It has been rated as very critical. This issue affects the function check_cond_jmp_op of the component BPF. The manipulation with an unknown input leads to a null pointer dereference vulnerability. Using CWE to declare the problem leads to CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: bpf: Mark the zero register precise for a register-form NULL check check_cond_jmp_op() accepts "if rA <op> rB" as a NULL check for a nullable pointer rA when rB is a scalar known to be zero, lifts PTR_MAYBE_NULL from rA in the corresponding branch and does not mark rB precise. Consider the following program: r0 = bpf_get_prandom_u32(); r6 = 1; /* the r6 == 0 path is explored first */ if (r0 == 0) goto 1f; r6 = 0; 1: r0 = bpf_map_lookup_elem(map, &0); /* absent, NULL at runtime */ if (r0 == r6) goto 2f; /* taken as a NULL check for r0 */ *(u8 *)(r0 + 0); /* verifier: map value; runtime: zero */ 2: return 0; The r6 == 0 path is explored first and the dereference is accepted. The r6 == 1 path is pruned at the checkpoint recorded for (1), so the comparison is never verified with a non-zero r6. At runtime a failed lookup returns NULL, NULL != 1 takes the non-NULL edge and the program dereferences a pointer that is zero.

It is possible to read the advisory at git.kernel.org. The identification of this vulnerability is CVE-2026-98040 since 09/25/2026. The exploitation is known to be easy. The attack may be initiated remotely. The exploitation requires an enhanced level of successful authentication. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/25/2026).

Upgrading to version 7.2.7 or 7.3-rc2 eliminates this vulnerability. Applying the patch ddca9a3b8833168dda3e62676648a636fb3f221c/6aed0134d3cda6382385a734ae0158eb7df6b142 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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