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GHSA-HCWG-2FCH-4V4C

Vulnerability from github – Published: 2026-09-25 12:31 – Updated: 2026-09-25 12:31

Details

In the Linux kernel, the following vulnerability has been resolved:

bpf: backtracking shouldn't clear outer frame R1-R5 for callbacks

When processing calls to bpf_loop() verifier marks R1 (and R4) as precise. R1 tracks loop iterations number and because of the 'callback_depth < R1' mechanics in check_helper_call() must be marked precise. However, precision propagation for R1 was broken, when bpf_loop() call was verified on a second iteration.

Consider the following verification trace: - main: bpf_loop(nr_loops, callback ...) - callback: BPF_EXIT - main: bpf_loop(nr_loops, callback ...) - ...

While the first visit of the call to bpf_loop() propagated R1 precision as expected, the second call to mark_chain_precision() in the check_helper_call() set R1, but it was immediately reset when backtrack_insn() processed preceding BPF_EXIT in the loop deleted in this patch.

Because of that, the second visit of the call to bpf_loop() injected checkpoint with R1 not marked as precise. Which could trick the verifier into accepting unsafe programs. See the next patch for an example of such program.

Commit is structured in a way to minimize conflicts when 'bpf' would be eventually merged with 'bpf-next'.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98084"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-25T11:17:37Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: backtracking shouldn\u0027t clear outer frame R1-R5 for callbacks\n\nWhen processing calls to bpf_loop() verifier marks R1 (and R4) as\nprecise. R1 tracks loop iterations number and because of the\n\u0027callback_depth \u003c R1\u0027 mechanics in check_helper_call() must be marked\nprecise. However, precision propagation for R1 was broken,\nwhen bpf_loop() call was verified on a second iteration.\n\nConsider the following verification trace:\n- main: bpf_loop(nr_loops, callback ...)\n- callback: BPF_EXIT\n- main: bpf_loop(nr_loops, callback ...)\n- ...\n\nWhile the first visit of the call to bpf_loop() propagated R1\nprecision as expected, the second call to mark_chain_precision() in\nthe check_helper_call() set R1, but it was immediately reset when\nbacktrack_insn() processed preceding BPF_EXIT in the loop deleted in\nthis patch.\n\nBecause of that, the second visit of the call to bpf_loop() injected\ncheckpoint with R1 not marked as precise. Which could trick the\nverifier into accepting unsafe programs. See the next patch for an\nexample of such program.\n\nCommit is structured in a way to minimize conflicts when\n\u0027bpf\u0027 would be eventually merged with \u0027bpf-next\u0027.",
  "id": "GHSA-hcwg-2fch-4v4c",
  "modified": "2026-09-25T12:31:36Z",
  "published": "2026-09-25T12:31:36Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98084"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e3e4f66cc4b72333d0886ae2673c360248987889"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f83890dfed9efc5e19df1dbc1ad707a142936923"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-98084 (GCVE-0-2026-98084)

Vulnerability from cvelistv5 – Published: 2026-09-25 10:24 – Updated: 2026-09-25 10:24

Title

bpf: backtracking shouldn't clear outer frame R1-R5 for callbacks

Summary

In the Linux kernel, the following vulnerability has been resolved: bpf: backtracking shouldn't clear outer frame R1-R5 for callbacks When processing calls to bpf_loop() verifier marks R1 (and R4) as precise. R1 tracks loop iterations number and because of the 'callback_depth < R1' mechanics in check_helper_call() must be marked precise. However, precision propagation for R1 was broken, when bpf_loop() call was verified on a second iteration. Consider the following verification trace: - main: bpf_loop(nr_loops, callback ...) - callback: BPF_EXIT - main: bpf_loop(nr_loops, callback ...) - ... While the first visit of the call to bpf_loop() propagated R1 precision as expected, the second call to mark_chain_precision() in the check_helper_call() set R1, but it was immediately reset when backtrack_insn() processed preceding BPF_EXIT in the loop deleted in this patch. Because of that, the second visit of the call to bpf_loop() injected checkpoint with R1 not marked as precise. Which could trick the verifier into accepting unsafe programs. See the next patch for an example of such program. Commit is structured in a way to minimize conflicts when 'bpf' would be eventually merged with 'bpf-next'.

Severity

No CVSS data available.

Assigner

Linux mitre root

References

2 references

URL	Tags
https://git.kernel.org/stable/c/f83890dfed9efc5e1…
https://git.kernel.org/stable/c/e3e4f66cc4b72333d…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: ab5cfac139ab8576fb54630d4cca23c3e690ee90 , < f83890dfed9efc5e19df1dbc1ad707a142936923 (git) Affected: ab5cfac139ab8576fb54630d4cca23c3e690ee90 , < e3e4f66cc4b72333d0886ae2673c360248987889 (git) Affected: b43550d7d58e7ae6618aaab18c1e912fa4d6e3dd (git) Affected: 6.6.15 , < 6.7 (semver)
Linux	Linux	Affected: 6.7 Unaffected: 0 , < 6.7 (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/backtrack.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "f83890dfed9efc5e19df1dbc1ad707a142936923",
              "status": "affected",
              "version": "ab5cfac139ab8576fb54630d4cca23c3e690ee90",
              "versionType": "git"
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            {
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              "status": "affected",
              "version": "ab5cfac139ab8576fb54630d4cca23c3e690ee90",
              "versionType": "git"
            },
            {
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              "version": "b43550d7d58e7ae6618aaab18c1e912fa4d6e3dd",
              "versionType": "git"
            },
            {
              "lessThan": "6.7",
              "status": "affected",
              "version": "6.6.15",
              "versionType": "semver"
            }
          ]
        },
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          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.7"
            },
            {
              "lessThan": "6.7",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.7",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
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              "versionType": "original_commit_for_fix"
            }
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      ],
      "cpeApplicability": [
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            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                },
                {
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                {
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      "descriptions": [
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: backtracking shouldn\u0027t clear outer frame R1-R5 for callbacks\n\nWhen processing calls to bpf_loop() verifier marks R1 (and R4) as\nprecise. R1 tracks loop iterations number and because of the\n\u0027callback_depth \u003c R1\u0027 mechanics in check_helper_call() must be marked\nprecise. However, precision propagation for R1 was broken,\nwhen bpf_loop() call was verified on a second iteration.\n\nConsider the following verification trace:\n- main: bpf_loop(nr_loops, callback ...)\n- callback: BPF_EXIT\n- main: bpf_loop(nr_loops, callback ...)\n- ...\n\nWhile the first visit of the call to bpf_loop() propagated R1\nprecision as expected, the second call to mark_chain_precision() in\nthe check_helper_call() set R1, but it was immediately reset when\nbacktrack_insn() processed preceding BPF_EXIT in the loop deleted in\nthis patch.\n\nBecause of that, the second visit of the call to bpf_loop() injected\ncheckpoint with R1 not marked as precise. Which could trick the\nverifier into accepting unsafe programs. See the next patch for an\nexample of such program.\n\nCommit is structured in a way to minimize conflicts when\n\u0027bpf\u0027 would be eventually merged with \u0027bpf-next\u0027."
        }
      ],
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        "dateUpdated": "2026-09-25T10:24:19.881Z",
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      ],
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    "cveId": "CVE-2026-98084",
    "datePublished": "2026-09-25T10:24:19.881Z",
    "dateReserved": "2026-09-25T10:19:56.075Z",
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    "state": "PUBLISHED"
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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GHSA-HCWG-2FCH-4V4C

CVE-2026-98084 (GCVE-0-2026-98084)

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