CVE-2026-98040 (GCVE-0-2026-98040)

Vulnerability from cvelistv5 – Published: 2026-09-25 10:23 – Updated: 2026-09-25 10:23
VLAI
Title
bpf: Mark the zero register precise for a register-form NULL check
Summary
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.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 2f4cb53eed448c1aeb6f4b40cf9c810716d8218c , < ddca9a3b8833168dda3e62676648a636fb3f221c (git)
Affected: 2f4cb53eed448c1aeb6f4b40cf9c810716d8218c , < 6aed0134d3cda6382385a734ae0158eb7df6b142 (git)
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Linux Linux Affected: 7.1
Unaffected: 0 , < 7.1 (semver)
Unaffected: 7.2.7 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc2 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/verifier.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "lessThan": "ddca9a3b8833168dda3e62676648a636fb3f221c",
              "status": "affected",
              "version": "2f4cb53eed448c1aeb6f4b40cf9c810716d8218c",
              "versionType": "git"
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              "versionType": "git"
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          "defaultStatus": "affected",
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          "vendor": "Linux",
          "versions": [
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              "version": "7.1"
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              "versionType": "semver"
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.7",
                  "versionStartIncluding": "7.1",
                  "vulnerable": true
                },
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                  "versionEndExcluding": "7.3-rc2",
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Mark the zero register precise for a register-form NULL check\n\ncheck_cond_jmp_op() accepts \"if rA \u003cop\u003e rB\" as a NULL check for a\nnullable pointer rA when rB is a scalar known to be zero,\nlifts PTR_MAYBE_NULL from rA in the corresponding branch and does not\nmark rB precise. Consider the following program:\n\n  r0 = bpf_get_prandom_u32();\n  r6 = 1;                  /* the r6 == 0 path is explored first */\n  if (r0 == 0) goto 1f;\n  r6 = 0;\n1:\n  r0 = bpf_map_lookup_elem(map, \u00260);  /* absent, NULL at runtime */\n  if (r0 == r6) goto 2f;   /* taken as a NULL check for r0       */\n  *(u8 *)(r0 + 0);         /* verifier: map value; runtime: zero */\n2:\n  return 0;\n\nThe r6 == 0 path is explored first and the dereference is accepted.\nThe r6 == 1 path is pruned at the checkpoint recorded for (1),\nso the comparison is never verified with a non-zero r6. At runtime a\nfailed lookup returns NULL, NULL != 1 takes the non-NULL edge and the\nprogram dereferences a pointer that is zero."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-25T10:23:53.001Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/ddca9a3b8833168dda3e62676648a636fb3f221c"
        },
        {
          "url": "https://git.kernel.org/stable/c/6aed0134d3cda6382385a734ae0158eb7df6b142"
        }
      ],
      "title": "bpf: Mark the zero register precise for a register-form NULL check",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98040",
    "datePublished": "2026-09-25T10:23:53.001Z",
    "dateReserved": "2026-09-25T10:19:56.071Z",
    "dateUpdated": "2026-09-25T10:23:53.001Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-98040",
      "date": "2026-09-26",
      "epss": "0.00189",
      "percentile": "0.0767"
    },
    "nvd": {
      "cve": {
        "affected": [
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                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
                  "kernel/bpf/verifier.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                    "status": "affected",
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                    "versionType": "git"
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                    "versionType": "git"
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              {
                "defaultStatus": "affected",
                "product": "Linux",
                "programFiles": [
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                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
                  {
                    "status": "affected",
                    "version": "7.1"
                  },
                  {
                    "lessThan": "7.1",
                    "status": "unaffected",
                    "version": "0",
                    "versionType": "semver"
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                  {
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                    "versionType": "semver"
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              }
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Mark the zero register precise for a register-form NULL check\n\ncheck_cond_jmp_op() accepts \"if rA \u003cop\u003e rB\" as a NULL check for a\nnullable pointer rA when rB is a scalar known to be zero,\nlifts PTR_MAYBE_NULL from rA in the corresponding branch and does not\nmark rB precise. Consider the following program:\n\n  r0 = bpf_get_prandom_u32();\n  r6 = 1;                  /* the r6 == 0 path is explored first */\n  if (r0 == 0) goto 1f;\n  r6 = 0;\n1:\n  r0 = bpf_map_lookup_elem(map, \u00260);  /* absent, NULL at runtime */\n  if (r0 == r6) goto 2f;   /* taken as a NULL check for r0       */\n  *(u8 *)(r0 + 0);         /* verifier: map value; runtime: zero */\n2:\n  return 0;\n\nThe r6 == 0 path is explored first and the dereference is accepted.\nThe r6 == 1 path is pruned at the checkpoint recorded for (1),\nso the comparison is never verified with a non-zero r6. At runtime a\nfailed lookup returns NULL, NULL != 1 takes the non-NULL edge and the\nprogram dereferences a pointer that is zero."
          }
        ],
        "id": "CVE-2026-98040",
        "lastModified": "2026-09-25T11:17:32.773",
        "metrics": {},
        "published": "2026-09-25T11:17:32.773",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/6aed0134d3cda6382385a734ae0158eb7df6b142"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/ddca9a3b8833168dda3e62676648a636fb3f221c"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    }
  }
}



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