CVE-2026-74583
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_route: fix fastmap use-after-free on filter The route4 classifier maintains a 16-slot fastmap cache that stores raw struct route4_filter pointers indexed by (id, iif).
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.12%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_route: fix fastmap use-after-free on filter The route4 classifier maintains a 16-slot fastmap cache that stores raw struct route4_filter pointers indexed by (id, iif). The reader (route4_classify) populates this cache via route4_set_fastmap() for every classified packet that hits a filter. The writer (route4_delete, route4_change) clears the cache via route4_reset_fastmap() before RCU-deferred kfree of the filter. This creates a UAF race: 1. Reader walks the RCU-protected bucket chain, finds filter f 2. Writer unlinks f, calls route4_reset_fastmap(), then tcf_queue_work() 3. Reader calls route4_set_fastmap() and writes f into the cache *after* the writer's reset, caching a pointer about to be freed 4. After the RCU grace period, kfree(f) executes 5. Next classified packet on the same (id, iif) tuple hits the stale fastmap entry and reads f->res from freed memory Reproduced with an mdelay(100) accelerator in route4_set_fastmap() and a concurrent add/delete stress test (provided by both zdi and Santosh). Both triggered KASAN slab-use-after-free reports in the route4 fastmap paths. Fix: Introduce a per-filter boolean dying flag to suppress stale fastmap republishing by in-flight readers.
- CVSS 3.1
- 7.8 HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 0.12% probability · 2th percentile
- CISA KEV
- Not listed
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
References
- https://git.kernel.org/stable/c/0e7a8cf8895b06d07c7311f028eba16ad742b9bc
- https://git.kernel.org/stable/c/47d7f7051253bdc02b1d245d87e38f16d31a74df
- https://git.kernel.org/stable/c/5ec9001be6d0eb527251125632ec8fe88278897f
- https://git.kernel.org/stable/c/7897198b26445b4009a057bda1986b94a99e5d5f
- https://git.kernel.org/stable/c/820f083c294ad6d319c02a7d43294f2ed2565139
- https://git.kernel.org/stable/c/a17f636c9330eac879822ce29f998e5abd1b72c1
- https://git.kernel.org/stable/c/ae9aff87025219005a2d16b4fe83d6f24643e50d
- https://git.kernel.org/stable/c/b969984b2bdc85d721ce4047cd270cd37ec705a2
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.