bpf: reject negative CO-RE accessor indices in bpf_core_parse_spec()

{
  "id": "17c0fb2c657f3cb09f4b51be41005ddba21954f7ed3e0a8f84ba6b0c25ec3d0d",
  "url": "https://osv.dev/vulnerability/CVE-2026-45839",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "bpf: reject negative CO-RE accessor indices in bpf_core_parse_spec()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: bpf: reject negative CO-RE accessor indices in bpf_core_parse_spec() CO-RE accessor strings are colon-separated indices that describe a path from a root BTF type to a target field, e.g. \"0:1:2\" walks through nested struct members. bpf_core_parse_spec() parses each component with sscanf(\"%d\"), so negative values like -1 are silently accepted. The subsequent bounds checks (access_idx >= btf_vlen(t)) only guard the upper bound and always pass for negative values because C integer promotion converts the __u16 btf_vlen result to int, making the comparison (int)(-1) >= (int)(N) false for any positive N. When -1 reaches btf_member_bit_offset() it gets cast to u32 0xffffffff, producing an out-of-bounds read far past the members array. A crafted BPF program with a negative CO-RE accessor on any struct that exists in vmlinux BTF (e.g. task_struct) crashes the kernel deterministically during BPF_PROG_LOAD on any system with CONFIG_DEBUG_INFO_BTF=y (default on major distributions). The bug is reachable with CAP_BPF: BUG: unable to handle page fault for address: ffffed11818b6626 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page Oops: Oops: 0000 [#1] SMP KASAN NOPTI CPU: 0 UID: 0 PID: 85 Comm: poc Not tainted 7.0.0-rc6 #18 PREEMPT(full) RIP: 0010:bpf_core_parse_spec (tools/lib/bpf/relo_core.c:354) RAX: 00000000ffffffff Call Trace: bpf_core_calc_relo_insn (tools/lib/bpf/relo_core.c:1321) ",
    "evidence": "osv:CVE-2026-45839",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.267",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.209",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.175",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.141",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.91",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.33",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.0.10",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-45839",
      "aliases": [
        "CVE-2026-45839"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                  "introduced": "ddc7c3042614e273044f698d2beab25cc3842d45"
                },
                {
                  "fixed": "c8e49b79c4b48bd687706ff6e9c82638dc81ef80"
                },
                {
                  "fixed": "a9e777f856cd2f1efc106afc7bf21aef868509d5"
                },
                {
                  "fixed": "669349b4612c26b3d7aacfa99d7174681bd19223"
                },
                {
                  "fixed": "3ff85ae79e1a74baeb916b78a63d821f6d19a994"
                },
                {
                  "fixed": "36a9012f76ba8d9189ae56a1f8bb7c87c07a1f3a"
                },
                {
                  "fixed": "76f2ebaf79a9ae6d0737b87f045fe769e425d78f"
                },
                {
                  "fixed": "99dbab7b5a12d8f58d5b0aa2f7a1fe656a70f4b2"
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                {
                  "fixed": "1c22483a2c4bbf747787f328392ca3e68619c4dc"
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              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-45839.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.4.0"
                },
                {
                  "fixed": "5.10.267"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.11.0"
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                {
                  "fixed": "5.15.209"
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                  "introduced": "5.16.0"
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                {
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                  "introduced": "6.2.0"
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              ]
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            {
              "type": "ECOSYSTEM",
              "events": [
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                  "introduced": "6.7.0"
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                {
                  "fixed": "6.12.91"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
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                  "introduced": "6.13.0"
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                {
                  "fixed": "6.18.33"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
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                  "introduced": "6.19.0"
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                {
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              ]
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-45839.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:24.580550823Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-784472.html",
        "https://git.kernel.org/stable/c/1c22483a2c4bbf747787f328392ca3e68619c4dc",
        "https://git.kernel.org/stable/c/36a9012f76ba8d9189ae56a1f8bb7c87c07a1f3a",
        "https://git.kernel.org/stable/c/3ff85ae79e1a74baeb916b78a63d821f6d19a994",
        "https://git.kernel.org/stable/c/669349b4612c26b3d7aacfa99d7174681bd19223",
        "https://git.kernel.org/stable/c/76f2ebaf79a9ae6d0737b87f045fe769e425d78f",
        "https://git.kernel.org/stable/c/99dbab7b5a12d8f58d5b0aa2f7a1fe656a70f4b2",
        "https://git.kernel.org/stable/c/a9e777f856cd2f1efc106afc7bf21aef868509d5",
        "https://git.kernel.org/stable/c/c8e49b79c4b48bd687706ff6e9c82638dc81ef80",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45839.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-45839",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45839.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-45839",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 490812,
  "published_at": "2026-05-27T09:24:37.855+00:00"
}