CVE-2026-74583

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.

Gravité et risque d'exploitation

CVE-2026-74583 obtient un score CVSS de 7.8/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.12 %, ce qui la place devant 1.5 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=6.1.*, 7.2, <=6.12.*, 6.6.152, 0, <=7.1.*, 5.15.216, 1109c00547fc66df45b9ff923544be4c1e1bec13, <820f083c294ad6d319c02a7d43294f2ed2565139, <=5.10.*, <=6.6.*, 7.1.9, <a17f636c9330eac879822ce29f998e5abd1b72c1, <ae9aff87025219005a2d16b4fe83d6f24643e50d, 6.1.183, <5ec9001be6d0eb527251125632ec8fe88278897f, <=6.18.*, 6.12.104, <3.18, 6.18.45, <=*, <=5.15.*, <0e7a8cf8895b06d07c7311f028eba16ad742b9bc, <b969984b2bdc85d721ce4047cd270cd37ec705a2, 5.10.265, <7897198b26445b4009a057bda1986b94a99e5d5f, <47d7f7051253bdc02b1d245d87e38f16d31a74df, 3.18) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/7897198b26445b4009a057bda1986b94a99e5d5f
• https://git.kernel.org/stable/c/820f083c294ad6d319c02a7d43294f2ed2565139
• https://git.kernel.org/stable/c/5ec9001be6d0eb527251125632ec8fe88278897f
• https://git.kernel.org/stable/c/b969984b2bdc85d721ce4047cd270cd37ec705a2
• https://git.kernel.org/stable/c/a17f636c9330eac879822ce29f998e5abd1b72c1
• https://git.kernel.org/stable/c/0e7a8cf8895b06d07c7311f028eba16ad742b9bc
• https://git.kernel.org/stable/c/ae9aff87025219005a2d16b4fe83d6f24643e50d
• https://git.kernel.org/stable/c/47d7f7051253bdc02b1d245d87e38f16d31a74df