FKIE_CVE-2026-90053

Vulnerability from fkie_nvd - Published: 2026-09-17 17:16 - Updated: 2026-10-19 09:18
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_htb: limit htb_classify inner-class filter hops htb_classify() follows each filter-selected inner class by switching to cl->filter_list, but never bounds the number of hops. A filter on an inner class can point back to itself or to another inner class that points back, creating an infinite loop in the packet classification path with the qdisc lock held and BH disabled — a soft lockup / panic from a single packet. Bound the traversal with a hop counter and drop the packet with a rate-limited warning once the bound is exceeded. The counter is incremented at the point the inner filter chain is picked up, after the TC_ACT_* switch has consumed the classifier verdict, so a terminal TC_ACT_QUEUED/STOLEN/TRAP on the last permitted chain still sets *qerr to __NET_XMIT_STOLEN and the packet is not charged as a drop by this qdisc or its parent. The bound is TC_HTB_MAXDEPTH, taken from HTB's own parameters rather than from the qdisc hierarchy depth limit. Class levels run from 0 to TC_HTB_MAXDEPTH - 1, so a traversal that strictly descends in level can take at most TC_HTB_MAXDEPTH hops. That descent is what a sane configuration does, but it is assumed here rather than enforced: htb_find() resolves a classid against every class in the qdisc, so a filter may equally select a sibling or an ancestor. The normal root -> inner -> leaf path takes a single hop, so the bound does not affect legitimate classification. htb_classify() can now return NULL irrespective of CONFIG_NET_CLS_ACT, whereas previously every NULL return sat inside that ifdef. The NULL handler in htb_enqueue() therefore cannot stay conditional either, so drop the ifdef around it. This matches hfsc_enqueue(), which has always handled a NULL class unconditionally. Without it, a kernel built without actions would dereference a NULL class instead of dropping. Conditions to recreate the bug: - CONFIG_NET_SCHED, CONFIG_NET_SCH_HTB, CONFIG_NET_CLS_U32, CONFIG_LOCKUP_DETECTOR. - Create an HTB qdisc on a device (e.g. lo), add an inner class 1:1 with a leaf child 1:10, install a root u32 filter selecting 1:1, and an inner-class u32 filter on 1:1 also selecting 1:1. - Send one packet (ping). On the unfixed kernel the classify loop spins with the qdisc lock held; with softlockup_panic=1 it panics. - Reachable from unprivileged user via unshare -Urn (CAP_NET_ADMIN).
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/010d05df52cec053bdc67d82c5b61cc4996f3fde
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/729c4896ab829169f95915d65edd530325910b37
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/83bb11805b620c498d6417e0e409f26887981489
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/872317e84fd019ceffba125e62d31586e3336d41
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/8c9611f7ba3ea5594e41bac952363aa0966d3280
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/90a149ab1f8344b7f713e9a838f69fde9e8d2a51
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/e54be9aa503a0297b63aec530fbf760350effd45
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sched/sch_htb.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "83bb11805b620c498d6417e0e409f26887981489",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "90a149ab1f8344b7f713e9a838f69fde9e8d2a51",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "010d05df52cec053bdc67d82c5b61cc4996f3fde",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "8c9611f7ba3ea5594e41bac952363aa0966d3280",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "e54be9aa503a0297b63aec530fbf760350effd45",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "872317e84fd019ceffba125e62d31586e3336d41",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "729c4896ab829169f95915d65edd530325910b37",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/sched/sch_htb.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.12"
            },
            {
              "lessThan": "2.6.12",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.221",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.188",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.110",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.52",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: sch_htb: limit htb_classify inner-class filter hops\n\nhtb_classify() follows each filter-selected inner class by switching\nto cl-\u003efilter_list, but never bounds the number of hops. A filter on\nan inner class can point back to itself or to another inner class that\npoints back, creating an infinite loop in the packet classification\npath with the qdisc lock held and BH disabled \u2014 a soft lockup / panic\nfrom a single packet.\n\nBound the traversal with a hop counter and drop the packet with a\nrate-limited warning once the bound is exceeded. The counter is\nincremented at the point the inner filter chain is picked up, after the\nTC_ACT_* switch has consumed the classifier verdict, so a terminal\nTC_ACT_QUEUED/STOLEN/TRAP on the last permitted chain still sets *qerr\nto __NET_XMIT_STOLEN and the packet is not charged as a drop by this\nqdisc or its parent.\n\nThe bound is TC_HTB_MAXDEPTH, taken from HTB\u0027s own parameters rather than\nfrom the qdisc hierarchy depth limit. Class levels run from 0 to\nTC_HTB_MAXDEPTH - 1, so a traversal that strictly descends in level can\ntake at most TC_HTB_MAXDEPTH hops. That descent is what a sane\nconfiguration does, but it is assumed here rather than enforced:\nhtb_find() resolves a classid against every class in the qdisc, so a\nfilter may equally select a sibling or an ancestor. The normal\nroot -\u003e inner -\u003e leaf path takes a single hop, so the bound does not\naffect legitimate classification.\n\nhtb_classify() can now return NULL irrespective of CONFIG_NET_CLS_ACT,\nwhereas previously every NULL return sat inside that ifdef. The NULL\nhandler in htb_enqueue() therefore cannot stay conditional either, so\ndrop the ifdef around it. This matches hfsc_enqueue(), which has always\nhandled a NULL class unconditionally. Without it, a kernel built\nwithout actions would dereference a NULL class instead of dropping.\n\nConditions to recreate the bug:\n- CONFIG_NET_SCHED, CONFIG_NET_SCH_HTB, CONFIG_NET_CLS_U32,\n  CONFIG_LOCKUP_DETECTOR.\n- Create an HTB qdisc on a device (e.g. lo), add an inner class\n  1:1 with a leaf child 1:10, install a root u32 filter selecting\n  1:1, and an inner-class u32 filter on 1:1 also selecting 1:1.\n- Send one packet (ping). On the unfixed kernel the classify loop\n  spins with the qdisc lock held; with softlockup_panic=1 it panics.\n- Reachable from unprivileged user via unshare -Urn (CAP_NET_ADMIN)."
    }
  ],
  "id": "CVE-2026-90053",
  "lastModified": "2026-10-19T09:18:53.537",
  "metrics": {},
  "published": "2026-09-17T17:16:53.723",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/010d05df52cec053bdc67d82c5b61cc4996f3fde"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/729c4896ab829169f95915d65edd530325910b37"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/83bb11805b620c498d6417e0e409f26887981489"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/872317e84fd019ceffba125e62d31586e3336d41"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/8c9611f7ba3ea5594e41bac952363aa0966d3280"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/90a149ab1f8344b7f713e9a838f69fde9e8d2a51"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e54be9aa503a0297b63aec530fbf760350effd45"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.

Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • 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.
Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

JSON
How durations are calculated

Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

Loading timeline…




    Related by attack behaviour

    Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.