CVE-2026-74583 Affecting linux-6.12 package, versions <6.12.107-1~deb12u1


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.12% (2nd percentile)

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  • Snyk IDSNYK-ECHOLATEST-LINUX612-19964241
  • published20 Sept 2026
  • disclosed21 Aug 2026

Introduced: 21 Aug 2026

CVE-2026-74583  (opens in a new tab)

How to fix?

Upgrade Echo:latest linux-6.12 to version 6.12.107-1~deb12u1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream linux-6.12 package and not the linux-6.12 package as distributed by Echo. See How to fix? for Echo:latest relevant fixed versions and status.

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 Base Scores

version 3.1