CVE-2026-98610

Status: ReceivedUnscored—

Severity—Unscored

Exploitation probability0.21 %higher than 11% of CVEs

Active exploitationNonot in the CISA catalog

Public exploitNot knownno public code found

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

net/sched: sch_hfsc: bound the classify inner-filter walk with a drift budget

hfsc_classify() applies the "filter may only point downwards" level check only when the filter result carries no bound class. A filter created with a flowid gets res.class set once at bind time, so the check never runs for it during classification. hfsc_adjust_levels() can later raise a class's level without revalidating existing bindings, leaving two binds that were each legal at bind time pointing at each other; the classify walk then bounces between two interior classes forever with the qdisc lock held and BH disabled — a soft lockup from a single packet. The stuck walk trips the watchdog:

Read full descriptionShow less

Bound the traversal with a budget of non-descending hops, the only way a configured walk can move without descending the class tree once levels drift after bind time. The budget is cumulative over the whole walk and is deliberately not reset on a descending hop: a chain that alternates a descent with a lateral hop would return the budget every lap and never trip. Descending hops never decrement it, so legitimately deep trees are unaffected and a terminating lateral chain still classifies normally. Drop the packet with a rate-limited warning once the budget is exhausted, mirroring the merged HTB fix.

This is a follow-up to commit 729c4896ab82 ("net/sched: sch_htb: limit htb_classify inner-class filter hops"), which bounded the same classify loop on the HTB side but left the HFSC walk unbounded.

Technical details traces, logs and code from the original report

  watchdog: BUG: soft lockup - CPU#3 stuck for 13s! [ping:444]
  RIP: 0010:u32_classify+0x542/0x17f0
  ...
  tcf_classify+0x66/0xa0
  hfsc_enqueue+0x166/0xdf0

Conditions to recreate the bug:
- CONFIG_NET_SCHED, CONFIG_NET_SCH_HFSC, CONFIG_NET_CLS_U32,
  CONFIG_LOCKUP_DETECTOR.
- Build a cycle with two legal-at-bind-time flowid binds and a level
  drift: class X 1:1 (child of root) with leaf child 1:10; class Y 1:2
  (sibling of X) with children 1:20 and 1:200; root u32 filter flowid
  1:1; filter on X flowid 1:2 (legal when Y is a leaf); after Y's level
  rises to 2, filter on Y flowid 1:1 (legal then). Send one packet (ping
  on the device). Unfixed kernel: classify spins with the qdisc lock
  held; with softlockup_panic=1 it panics.
- Reachable from unprivileged user via unshare -Urn (CAP_NET_ADMIN).

CVSS

NVD hasn't assigned a CVSS score to this CVE (common since the April 2026 policy change).

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days: 0.21 %
Percentile among all scored CVEs: 11
Score date: 10/19/2026

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

Affected technologies (1)

⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.

Linux — Linux Kernel^AI

References

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Raw JSON (NVD)

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{
  "id": "CVE-2026-98610",
  "cveTags": [],
  "metrics": {},
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
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          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "a2f79227138c71e08627af5f8961197364edbc98",
              "lessThan": "d4fd251e3311727c32af89344d3332f788c153a2",
              "versionType": "git"
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              "versionType": "git"
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            {
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              "lessThan": "f476fb656ca2326d7b2eba98d03ced1cbcf5cd99",
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              "lessThan": "e8f9979286f70dfbfe0552e2a63000950841bea6",
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            {
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          "programFiles": [
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          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
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              "status": "affected",
              "version": "2.6.35"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "2.6.35",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "5.10.271",
              "versionType": "semver",
              "lessThanOrEqual": "5.10.*"
            },
            {
              "status": "unaffected",
              "version": "5.15.222",
              "versionType": "semver",
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            },
            {
              "status": "unaffected",
              "version": "6.1.189",
              "versionType": "semver",
              "lessThanOrEqual": "6.1.*"
            },
            {
              "status": "unaffected",
              "version": "6.6.158",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
              "status": "unaffected",
              "version": "6.12.112",
              "versionType": "semver",
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            },
            {
              "status": "unaffected",
              "version": "6.18.55",
              "versionType": "semver",
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            },
            {
              "status": "unaffected",
              "version": "7.2.9",
              "versionType": "semver",
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            },
            {
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "net/sched/sch_hfsc.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-10-18T16:17:13.793",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/0fa25ba50a382d79c0cf060214c2095756836f5f",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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    {
      "url": "https://git.kernel.org/stable/c/1301a1292c6742b4c96a18715d49f89c3caca0d7",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/2bd20245dd658789d8cccb37697967b4caba6ad8",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/30d7fea767e830bd81ac2f73d2e33c877cb2e679",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/8a60ade2277e1f0e0d0578d565354e52292fa46d",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/d4fd251e3311727c32af89344d3332f788c153a2",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/e8f9979286f70dfbfe0552e2a63000950841bea6",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/f476fb656ca2326d7b2eba98d03ced1cbcf5cd99",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: sch_hfsc: bound the classify inner-filter walk with a drift budget\n\nhfsc_classify() applies the \"filter may only point downwards\" level check\nonly when the filter result carries no bound class. A filter created with\na flowid gets res.class set once at bind time, so the check never runs for\nit during classification. hfsc_adjust_levels() can later raise a class's\nlevel without revalidating existing bindings, leaving two binds that were\neach legal at bind time pointing at each other; the classify walk then\nbounces between two interior classes forever with the qdisc lock held and\nBH disabled — a soft lockup from a single packet. The stuck walk trips\nthe watchdog:\n\n  watchdog: BUG: soft lockup - CPU#3 stuck for 13s! [ping:444]\n  RIP: 0010:u32_classify+0x542/0x17f0\n  ...\n  tcf_classify+0x66/0xa0\n  hfsc_enqueue+0x166/0xdf0\n\nBound the traversal with a budget of non-descending hops, the only way a\nconfigured walk can move without descending the class tree once levels\ndrift after bind time. The budget is cumulative over the whole walk and\nis deliberately not reset on a descending hop: a chain that alternates a\ndescent with a lateral hop would return the budget every lap and never\ntrip. Descending hops never decrement it, so legitimately deep trees are\nunaffected and a terminating lateral chain still classifies normally.\nDrop the packet with a rate-limited warning once the budget is exhausted,\nmirroring the merged HTB fix.\n\nThis is a follow-up to commit 729c4896ab82 (\"net/sched: sch_htb: limit\nhtb_classify inner-class filter hops\"), which bounded the same classify\nloop on the HTB side but left the HFSC walk unbounded.\n\nConditions to recreate the bug:\n- CONFIG_NET_SCHED, CONFIG_NET_SCH_HFSC, CONFIG_NET_CLS_U32,\n  CONFIG_LOCKUP_DETECTOR.\n- Build a cycle with two legal-at-bind-time flowid binds and a level\n  drift: class X 1:1 (child of root) with leaf child 1:10; class Y 1:2\n  (sibling of X) with children 1:20 and 1:200; root u32 filter flowid\n  1:1; filter on X flowid 1:2 (legal when Y is a leaf); after Y's level\n  rises to 2, filter on Y flowid 1:1 (legal then). Send one packet (ping\n  on the device). Unfixed kernel: classify spins with the qdisc lock\n  held; with softlockup_panic=1 it panics.\n- Reachable from unprivileged user via unshare -Urn (CAP_NET_ADMIN)."
    }
  ],
  "lastModified": "2026-10-19T10:19:23.103",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}