CVE-2026-98040
bpf: Mark the zero register precise for a register-form NULL check
Description
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.
INFO
Published Date :
Sept. 25, 2026, 11:17 a.m.
Last Modified :
Sept. 25, 2026, 11:17 a.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Solution
- Update the Linux kernel to the latest stable version.
- Apply the relevant security patch for the bpf module.
- Recompile and redeploy affected kernel modules.
- Verify the fix by testing the scenario.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-98040.
| URL | Resource |
|---|---|
| https://git.kernel.org/stable/c/6aed0134d3cda6382385a734ae0158eb7df6b142 | |
| https://git.kernel.org/stable/c/ddca9a3b8833168dda3e62676648a636fb3f221c |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-98040 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-98040
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-98040 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-98040 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Sep. 25, 2026
Action Type Old Value New Value Added Description 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. Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/98xxx/CVE-2026-98040.json">CVE-2026-98040</a> Added Reference https://git.kernel.org/stable/c/6aed0134d3cda6382385a734ae0158eb7df6b142 Added Reference https://git.kernel.org/stable/c/ddca9a3b8833168dda3e62676648a636fb3f221c