{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-74583","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-08-15T05:44:03.918Z","datePublished":"2026-08-21T16:31:55.886Z","dateUpdated":"2026-08-25T05:40:10.077Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-25T05:40:10.077Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: cls_route: fix fastmap use-after-free on filter\n\nThe route4 classifier maintains a 16-slot fastmap cache that stores raw\nstruct route4_filter pointers indexed by (id, iif). The reader\n(route4_classify) populates this cache via route4_set_fastmap() for every\nclassified packet that hits a filter. The writer (route4_delete,\nroute4_change) clears the cache via route4_reset_fastmap() before\nRCU-deferred kfree of the filter.\n\nThis creates a UAF race:\n 1. Reader walks the RCU-protected bucket chain, finds filter f\n 2. Writer unlinks f, calls route4_reset_fastmap(), then tcf_queue_work()\n 3. Reader calls route4_set_fastmap() and writes f into the cache\n    *after* the writer's reset, caching a pointer about to be freed\n 4. After the RCU grace period, kfree(f) executes\n 5. Next classified packet on the same (id, iif) tuple hits the stale\n    fastmap entry and reads f->res from freed memory\n\nReproduced with an mdelay(100) accelerator in route4_set_fastmap() and a\nconcurrent add/delete stress test (provided by both zdi and Santosh).\nBoth triggered KASAN slab-use-after-free reports in the route4 fastmap\npaths.\n\nFix:\nIntroduce a per-filter boolean dying flag to suppress stale fastmap\nrepublishing by in-flight readers."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - Exploitation requires local rtnetlink RTM_NEWTFILTER/RTM_DELTFILTER (tc filter add/change/del route) through sendmsg→rtnetlink_rcv_msg→tc_new_tfilter/tc_del_tfilter→route4_change/route4_delete; remote packets alone cannot trigger the filter-deletion side of the race.\nAC:L - The attacker controls both race sides—concurrent route filter add/change/delete via netlink plus traffic through route4_classify on clsact/ingress/egress qdiscs; ZDI and independent reporter stress tests reproduced KASAN slab-use-after-free without uncontrollable prerequisites.\nPR:L - Non-GET rtnetlink handlers require netlink_net_capable(CAP_NET_ADMIN), evaluated against the target network namespace user_ns; an unprivileged local user obtains CAP_NET_ADMIN via user+network namespaces (unshare -Urn) and configures clsact with route filters.\nUI:N - No victim interaction is needed; the attacker configures the route classifier, drives concurrent filter churn, and generates matching traffic from their own processes.\nS:U - Impact is kernel memory corruption within the same kernel security boundary (local privilege escalation/DoS); it does not cross VM, hypervisor, or IOMMU boundaries.\nC:H - Slab use-after-free: a stale fastmap entry retains a freed route4_filter pointer and route4_classify dereferences f->res from freed kmalloc memory; KASAN confirmed slab-use-after-free, enabling arbitrary kernel read via heap reclaim/spray.\nI:H - UAF of the kmalloc route4_filter object allows attacker-controlled heap spraying to reclaim the freed slot and obtain write/control-flow hijacking primitives; memory corruption is exploitable beyond a simple crash.\nA:H - UAF on the fastmap hot path causes kernel oops/panic under concurrent filter churn; KASAN slab-use-after-free was confirmed during add/delete stress testing, providing reliable denial of service even without full exploitation."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/cls_route.c"],"versions":[{"version":"1109c00547fc66df45b9ff923544be4c1e1bec13","lessThan":"7897198b26445b4009a057bda1986b94a99e5d5f","status":"affected","versionType":"git"},{"version":"1109c00547fc66df45b9ff923544be4c1e1bec13","lessThan":"820f083c294ad6d319c02a7d43294f2ed2565139","status":"affected","versionType":"git"},{"version":"1109c00547fc66df45b9ff923544be4c1e1bec13","lessThan":"5ec9001be6d0eb527251125632ec8fe88278897f","status":"affected","versionType":"git"},{"version":"1109c00547fc66df45b9ff923544be4c1e1bec13","lessThan":"b969984b2bdc85d721ce4047cd270cd37ec705a2","status":"affected","versionType":"git"},{"version":"1109c00547fc66df45b9ff923544be4c1e1bec13","lessThan":"a17f636c9330eac879822ce29f998e5abd1b72c1","status":"affected","versionType":"git"},{"version":"1109c00547fc66df45b9ff923544be4c1e1bec13","lessThan":"0e7a8cf8895b06d07c7311f028eba16ad742b9bc","status":"affected","versionType":"git"},{"version":"1109c00547fc66df45b9ff923544be4c1e1bec13","lessThan":"ae9aff87025219005a2d16b4fe83d6f24643e50d","status":"affected","versionType":"git"},{"version":"1109c00547fc66df45b9ff923544be4c1e1bec13","lessThan":"47d7f7051253bdc02b1d245d87e38f16d31a74df","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/cls_route.c"],"versions":[{"version":"3.18","status":"affected"},{"version":"0","lessThan":"3.18","status":"unaffected","versionType":"semver"},{"version":"5.10.265","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.15.216","lessThanOrEqual":"5.15.*","status":"unaffected","versionType":"semver"},{"version":"6.1.183","lessThanOrEqual":"6.1.*","status":"unaffected","versionType":"semver"},{"version":"6.6.152","lessThanOrEqual":"6.6.*","status":"unaffected","versionType":"semver"},{"version":"6.12.104","lessThanOrEqual":"6.12.*","status":"unaffected","versionType":"semver"},{"version":"6.18.45","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.1.9","lessThanOrEqual":"7.1.*","status":"unaffected","versionType":"semver"},{"version":"7.2","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"5.10.265"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"5.15.216"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.1.183"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.6.152"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.12.104"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.18.45"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"7.1.9"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"7.2"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/7897198b26445b4009a057bda1986b94a99e5d5f"},{"url":"https://git.kernel.org/stable/c/820f083c294ad6d319c02a7d43294f2ed2565139"},{"url":"https://git.kernel.org/stable/c/5ec9001be6d0eb527251125632ec8fe88278897f"},{"url":"https://git.kernel.org/stable/c/b969984b2bdc85d721ce4047cd270cd37ec705a2"},{"url":"https://git.kernel.org/stable/c/a17f636c9330eac879822ce29f998e5abd1b72c1"},{"url":"https://git.kernel.org/stable/c/0e7a8cf8895b06d07c7311f028eba16ad742b9bc"},{"url":"https://git.kernel.org/stable/c/ae9aff87025219005a2d16b4fe83d6f24643e50d"},{"url":"https://git.kernel.org/stable/c/47d7f7051253bdc02b1d245d87e38f16d31a74df"}],"title":"net/sched: cls_route: fix fastmap use-after-free on filter","x_generator":{"engine":"bippy-1.2.0"}}}}