{"api_version":"1","generated_at":"2026-09-20T02:46:07+00:00","cve":"CVE-2026-90053","urls":{"html":"https://cve.report/CVE-2026-90053","api":"https://cve.report/api/cve/CVE-2026-90053.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-90053","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-90053"},"summary":{"title":"net/sched: sch_htb: limit htb_classify inner-class filter hops","description":"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->filter_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 — 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's 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 -> inner -> 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).","state":"PUBLISHED","assigner":"Linux","published_at":"2026-09-17 17:16:53","updated_at":"2026-09-17 17:16:53"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/010d05df52cec053bdc67d82c5b61cc4996f3fde","name":"https://git.kernel.org/stable/c/010d05df52cec053bdc67d82c5b61cc4996f3fde","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/90a149ab1f8344b7f713e9a838f69fde9e8d2a51","name":"https://git.kernel.org/stable/c/90a149ab1f8344b7f713e9a838f69fde9e8d2a51","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/8c9611f7ba3ea5594e41bac952363aa0966d3280","name":"https://git.kernel.org/stable/c/8c9611f7ba3ea5594e41bac952363aa0966d3280","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/729c4896ab829169f95915d65edd530325910b37","name":"https://git.kernel.org/stable/c/729c4896ab829169f95915d65edd530325910b37","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/872317e84fd019ceffba125e62d31586e3336d41","name":"https://git.kernel.org/stable/c/872317e84fd019ceffba125e62d31586e3336d41","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/e54be9aa503a0297b63aec530fbf760350effd45","name":"https://git.kernel.org/stable/c/e54be9aa503a0297b63aec530fbf760350effd45","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/83bb11805b620c498d6417e0e409f26887981489","name":"https://git.kernel.org/stable/c/83bb11805b620c498d6417e0e409f26887981489","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-90053","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-90053","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 83bb11805b620c498d6417e0e409f26887981489 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 90a149ab1f8344b7f713e9a838f69fde9e8d2a51 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 010d05df52cec053bdc67d82c5b61cc4996f3fde git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 8c9611f7ba3ea5594e41bac952363aa0966d3280 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 e54be9aa503a0297b63aec530fbf760350effd45 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 872317e84fd019ceffba125e62d31586e3336d41 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 729c4896ab829169f95915d65edd530325910b37 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 2.6.12","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 2.6.12 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.15.221 5.15.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.1.188 6.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.6.157 6.6.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.110 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.52 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2.6 7.2.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.3-rc1 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"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-rc1","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.15.221","versionStartIncluding":"2.6.12","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.1.188","versionStartIncluding":"2.6.12","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.6.157","versionStartIncluding":"2.6.12","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.110","versionStartIncluding":"2.6.12","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.52","versionStartIncluding":"2.6.12","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2.6","versionStartIncluding":"2.6.12","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.3-rc1","versionStartIncluding":"2.6.12","vulnerable":true}],"negate":false,"operator":"OR"}]}],"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->filter_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 — 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's 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 -> inner -> 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)."}],"providerMetadata":{"dateUpdated":"2026-09-17T16:05:38.957Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/83bb11805b620c498d6417e0e409f26887981489"},{"url":"https://git.kernel.org/stable/c/90a149ab1f8344b7f713e9a838f69fde9e8d2a51"},{"url":"https://git.kernel.org/stable/c/010d05df52cec053bdc67d82c5b61cc4996f3fde"},{"url":"https://git.kernel.org/stable/c/8c9611f7ba3ea5594e41bac952363aa0966d3280"},{"url":"https://git.kernel.org/stable/c/e54be9aa503a0297b63aec530fbf760350effd45"},{"url":"https://git.kernel.org/stable/c/872317e84fd019ceffba125e62d31586e3336d41"},{"url":"https://git.kernel.org/stable/c/729c4896ab829169f95915d65edd530325910b37"}],"title":"net/sched: sch_htb: limit htb_classify inner-class filter hops","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-90053","datePublished":"2026-09-17T16:05:38.957Z","dateReserved":"2026-09-11T19:38:34.783Z","dateUpdated":"2026-09-17T16:05:38.957Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-09-17 17:16:53","lastModifiedDate":"2026-09-17 17:16:53","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"90053","Ordinal":"1","Title":"net/sched: sch_htb: limit htb_classify inner-class filter hops","CVE":"CVE-2026-90053","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"90053","Ordinal":"1","NoteData":"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->filter_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 — 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's 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 -> inner -> 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).","Type":"Description","Title":"net/sched: sch_htb: limit htb_classify inner-class filter hops"}]}}}