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bpf: check_cond_jmp_op(): properly infer if register is null

Assessment

Severity
Moderate
CVSS base score
5.5CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H/E:U
Impact
Not stated
EPSS · 30-day forecast
No EPSS score collected
Public detection template
No Nuclei template is listed in the current collected catalog
Exploitation detected
Unknown: not stated by MSRC
Exploitability
Not assessed
Publicly disclosed
Unknown: not stated by MSRC
Customer action
Required: follow the MSRC remediation guidance
Component
Mariner
Weakness
—
Issued by
Linux
Published
27 Sep 2026 · September 2026
Last revised
5 Nov 2026Information published.
CVSS 3.1 base metricsRed raises the risk · green lowers it
Attack vector
LocalAV:L
Attack complexity
LowAC:L
Privileges required
LowPR:L
User interaction
NoneUI:N
Scope
UnchangedS:U
Confidentiality
NoneC:N
Integrity
NoneI:N
Availability
HighA:H

Updates that fix it

0 KBs

No KB listed

No KB update is listed in the collected MSRC record. Check the MSRC advisory for product releases and other remedies.

Affected products

Open Source Software
3 affected products
  • azl3 kernel 6.6.157.1-1 on Azure Linux 3.0
  • azl3 kernel 6.6.159.1-1 on Azure Linux 3.0
  • azl3 kernel 6.6.161.1-1 on Azure Linux 3.0

What changed

  1. Detection template: Unknown: detection-template evidence is incomplete or retained → No Nuclei template listed
  2. Detection template: No Nuclei template listed → Unknown: detection-template evidence is incomplete or retained
  3. Affected products: azl3 kernel 6.6.157.1-1 on Azure Linux 3.0, azl3 kernel 6.6.159.1-1 on Azure Linux 3.0 → azl3 kernel 6.6.157.1-1 on Azure Linux 3.0, azl3 kernel 6.6.159.1-1 on Azure Linux 3.0, azl3 kernel 6.6.161.1-1 on Azure Linux 3.0
  4. Detection template: Unknown: detection-template evidence is incomplete or retained → No Nuclei template listed
  5. Detection template: No Nuclei template listed → Unknown: detection-template evidence is incomplete or retained
  6. Affected products: azl3 kernel 6.6.157.1-1 on Azure Linux 3.0 → azl3 kernel 6.6.157.1-1 on Azure Linux 3.0, azl3 kernel 6.6.159.1-1 on Azure Linux 3.0
  7. Detection template: No Nuclei template listed · Customer action: Required: apply the update → Required: follow the MSRC remediation guidance · Public disclosure: No → Unknown: not stated by MSRC · Exploitation detected: Not reported by MSRC → Unknown: not stated by MSRC
  8. Detection template: Unknown: exploit-code evidence is incomplete or retained → No Nuclei template listed · CISA KEV: Unknown: catalog evidence is incomplete or retained → Not listed in the collected catalog
  9. Detection template: No Nuclei template listed → Unknown: exploit-code evidence is incomplete or retained · CISA KEV: Not listed in the collected catalog → Unknown: catalog evidence is incomplete or retained
Page history

Changes are dated when recorded; day views use the last saved version from that UTC day, and citations stay fixed.

Cite this version
Field-level log (40)

Up to 100 recent field edits are shown; older edits may be outside retention.

  1. 6 Nov 2026 · 17:32:22 UTC Public detection templateUnknown: detection-template evidence is incomplete or retained → No Nuclei template listed
  2. 6 Nov 2026 · 17:32:22 UTC Source coverage: public-exploit-codeIncomplete → Current
  3. 6 Nov 2026 · 17:32:22 UTC Source coverage: first-epssIncomplete → Current
  4. 6 Nov 2026 · 17:32:22 UTC Source coverage: msrc-cvrfIncomplete → Current
  5. 6 Nov 2026 · 16:31:02 UTC Public detection templateNo Nuclei template listed → Unknown: detection-template evidence is incomplete or retained
  6. 6 Nov 2026 · 16:31:02 UTC Source coverage: public-exploit-codeCurrent → Incomplete
  7. 6 Nov 2026 · 16:31:02 UTC Source coverage: first-epssCurrent → Incomplete
  8. 6 Nov 2026 · 16:31:02 UTC Source coverage: msrc-cvrfCurrent → Incomplete
  9. 6 Nov 2026 · 09:07:49 UTC Last revised1 Nov 2026 14:52 UTC → 5 Nov 2026 14:51 UTC
  10. 6 Nov 2026 · 09:07:49 UTC Affected productsazl3 kernel 6.6.157.1-1 on Azure Linux 3.0, azl3 kernel 6.6.159.1-1 on Azure Linux 3.0 → azl3 kernel 6.6.157.1-1 on Azure Linux 3.0, azl3 kernel 6.6.159.1-1 on Azure Linux 3.0, azl3 kernel 6.6.161.1-1 on Azure Linux 3.0
  11. 2 Nov 2026 · 17:30:39 UTC Public detection templateUnknown: detection-template evidence is incomplete or retained → No Nuclei template listed
  12. 2 Nov 2026 · 17:30:39 UTC Source coverage: public-exploit-codeIncomplete → Current
  13. 2 Nov 2026 · 17:30:39 UTC Source coverage: first-epssIncomplete → Current
  14. 2 Nov 2026 · 17:30:39 UTC Source coverage: msrc-cvrfIncomplete → Current
  15. 2 Nov 2026 · 16:27:39 UTC Public detection templateNo Nuclei template listed → Unknown: detection-template evidence is incomplete or retained
  16. 2 Nov 2026 · 16:27:39 UTC Source coverage: public-exploit-codeCurrent → Incomplete
  17. 2 Nov 2026 · 16:27:39 UTC Source coverage: first-epssCurrent → Incomplete
  18. 2 Nov 2026 · 16:27:39 UTC Source coverage: msrc-cvrfCurrent → Incomplete
  19. 2 Nov 2026 · 09:04:36 UTC Last revised21 Oct 2026 18:41 UTC → 1 Nov 2026 14:52 UTC
  20. 2 Nov 2026 · 09:04:36 UTC Affected productsazl3 kernel 6.6.157.1-1 on Azure Linux 3.0 → azl3 kernel 6.6.157.1-1 on Azure Linux 3.0, azl3 kernel 6.6.159.1-1 on Azure Linux 3.0
  21. 29 Oct 2026 · 20:19:26 UTC Public detection templateNo Nuclei template listed
  22. 29 Oct 2026 · 20:19:26 UTC EPSSNot scored → No EPSS score collected
  23. 29 Oct 2026 · 20:19:26 UTC Customer actionRequired: apply the update → Required: follow the MSRC remediation guidance
  24. 29 Oct 2026 · 20:19:26 UTC Publicly disclosedNo → Unknown: not stated by MSRC
  25. 29 Oct 2026 · 20:19:26 UTC Exploitation detectedNot reported by MSRC → Unknown: not stated by MSRC
  26. 23 Oct 2026 · 09:33:49 UTC Public exploit codeUnknown: exploit-code evidence is incomplete or retained → No Nuclei template listed
  27. 23 Oct 2026 · 09:33:49 UTC CISA KEVUnknown: catalog evidence is incomplete or retained → Not listed in the collected catalog
  28. 23 Oct 2026 · 09:33:49 UTC Source coverage: public-exploit-codeIncomplete → Current
  29. 23 Oct 2026 · 09:33:49 UTC Source coverage: first-epssIncomplete → Current
  30. 23 Oct 2026 · 09:33:49 UTC Source coverage: cisa-kevIncomplete → Current
  31. 23 Oct 2026 · 09:33:49 UTC Source coverage: msrc-cvrfIncomplete → Current
  32. 23 Oct 2026 · 08:31:50 UTC Public exploit codeNo Nuclei template listed → Unknown: exploit-code evidence is incomplete or retained
  33. 23 Oct 2026 · 08:31:50 UTC CISA KEVNot listed in the collected catalog → Unknown: catalog evidence is incomplete or retained
  34. 23 Oct 2026 · 08:31:50 UTC Source coverage: public-exploit-codeCurrent → Incomplete
  35. 23 Oct 2026 · 08:31:50 UTC Source coverage: first-epssCurrent → Incomplete
  36. 23 Oct 2026 · 08:31:50 UTC Source coverage: cisa-kevCurrent → Incomplete
  37. 23 Oct 2026 · 08:31:50 UTC Source coverage: msrc-cvrfCurrent → Incomplete
  38. 21 Oct 2026 · 20:45:25 UTC Last revised28 Sep 2026 00:03 UTC → 21 Oct 2026 18:41 UTC
  39. 18 Oct 2026 · 14:54:30 UTC Link: September 2026/security?release=2026-Sep#cves
  40. 14 Oct 2026 · 11:22:42 UTC Source coverage: msrc-cvrfIncomplete → Current

Explore global source statements, affected packages and advisory history for CVE-2026-98134. The catalog has a separate collection scope from Microsoft release records.

Collected exploitation and prediction evidence

Risk source coverage

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

cve-program · CVE-2026-98134

Published

bpf: check_cond_jmp_op(): properly infer if register is null

In the Linux kernel, the following vulnerability has been resolved: bpf: check_cond_jmp_op(): properly infer if register is null Nicholas Carlini reported a bug when verifier can incorrectly infer that a pointer is non-null. The bug occurs when two pointers are compared and one of them has a type w/o PTR_MAYBE_NULL flag, but which allows a value to be NULL at runtime. Here is an example: // `a` is PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED // `a` is 0 at runtime. // `b` is PTR_TO_MAP_VALUE | PTR_MAYBE_NULL void *a = bpf_rdonly_cast(0, 0); int *b = bpf_map_lookup_elem(...); if (a == b) *b = 42; // verifier does not catch null pointer dereference This happens because of a special case in check_cond_jmp_op(), which attempts to strip PTR_MAYBE_NULL flags from pointer types, when processing comparisons like `rA == rB`, if either rA or rB can't be null. The non-null property is derived based on the absence of PTR_MAYBE_NULL flag on rA's or rB's type. But that is not sufficient for types like PTR_TO_MEM, as in the example. This patch replaces type_may_be_null() call with reg_not_null(), which contains an allowlist of types for which absence of PTR_MAYBE_NULL actually means that the value can't be NULL at runtime. At the moment, the list in the reg_not_null() omits two types for which PTR_MAYBE_NULL is applicable: PTR_TO_XDP_SOCK and PTR_TO_BUF. In order to remain backward compatible, and assuming that only comparison between pointers of the same type makes sense, this commit extends reg_not_null(). W/o such an extension e.g. verifier_jeq_infer_not_null/null_ptr_to_map_value fails. reg_not_null() can be extended further, but I deem that out of scope for the fix at hand. Explicit base_type(...) != PTR_TO_BTF_ID checks in the check_cond_jmp_op() can be removed with migration to reg_not_null(), but that is a behavioural change, as the special case would start matching for PTR_TO_BTF_ID that is also is_trusted_reg(). I omit the behavioural change from this commit.

Source published
25 Sep 2026 10:36:12 UTC
Source modified
21 Oct 2026 12:54:40 UTC
Observed here
23 Oct 2026 15:48:27 UTC
Source terms
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