{"id":"CVE-2026-74583","title":"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 indexe…","summary":"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 indexe…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","published":"2026-08-21","updated":"2026-10-14","sourceUpdated":"2026-10-14T19:10:00.297","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-74583","references":[{"url":"https://git.kernel.org/stable/c/0e7a8cf8895b06d07c7311f028eba16ad742b9bc","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/47d7f7051253bdc02b1d245d87e38f16d31a74df","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/5ec9001be6d0eb527251125632ec8fe88278897f","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/7897198b26445b4009a057bda1986b94a99e5d5f","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/820f083c294ad6d319c02a7d43294f2ed2565139","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/a17f636c9330eac879822ce29f998e5abd1b72c1","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/ae9aff87025219005a2d16b4fe83d6f24643e50d","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/b969984b2bdc85d721ce4047cd270cd37ec705a2","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"tags":["nvd"],"epss":0.00117,"epssPercentile":0.0155,"ingestedAt":"2026-10-14T19:49:57.561Z","slug":"CVE-2026-74583","body":"## Overview\n\nIn 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}