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CVE-2026-97959

Linux: net/sched: cls_route: free emptied bucket on filter move

Linux LinuxOperating systems
Open in ThreatlineRecord JSON
CVSS
NoneNot scored
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.18%Chance of exploitation activity in the next 30 days, higher than 6% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in9e7741b41a25b9d49df4d262fa314342e6f95c50Also 48d38bf8c22a05fde07ba1f885cde27b851649a2, 41e94079200aaf0cdbe4594b0af75710b33da124 and 3 moreCVE List
Published25 Sep 2026Updated 19 Oct 2026CVE List

What fixes it

  • 9e7741b41a25b9d49df4d262fa314342e6f95c50LinuxCVE List
  • 48d38bf8c22a05fde07ba1f885cde27b851649a2LinuxCVE List
  • 41e94079200aaf0cdbe4594b0af75710b33da124LinuxCVE List
  • 2e2f130951d34871b0643bf700164d97cff4b427LinuxCVE List
  • 81dd117c04422c6d0c7974aba9fa6a0ba370959bLinuxCVE List
  • 1853f30cf5c84971f99788a76207c6f745380896LinuxCVE List

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Description

In the Linux kernel, the following vulnerability has been resolved:

net/sched: cls_route: free emptied bucket on filter move

route4_change can move an existing filter to a different top-level bucket: route4_set_parms recomputes the handle from TCA_ROUTE4_TO/ FROM/IIF, and the handle-mismatch check is gated on the 'new' flag, so for an existing filter the new handle may differ from the old one and land in a different bucket. When this happens, the filter is unlinked from the old bucket, but the bucket itself is never freed once it goes empty. The stale empty bucket remains in head->table[], causing route4_delete to report *last=false even after the last live filter is gone. That pins the empty tcf_proto and causes a leak.

Fix this by refcounting the filters linked to a bucket and freeing the bucket when the count drops to zero. The existing scan in route4_delete goes away with it.

The count is updated at all sites that link or unlink a filter during add, change and delete, and the bucket is dropped from head->table[] as soon as it reaches zero.

Conditions to recreate the bug: CONFIG_NET_CLS_ROUTE4=y, CONFIG_NET_SCH_INGRESS=y, CONFIG_NET_CLS_ACT=y.

tc qdisc replace dev lo clsact tc filter add dev lo ingress protocol ip pref 100 route from 1 to 1 tc filter change dev lo ingress protocol ip pref 100 handle 0x10001 \ route from 1 to 2 tc filter del dev lo ingress protocol ip pref 100 handle 0x10002 \ route from 1 to 2 tc filter show dev lo ingress | grep -c 'pref 100 route chain 0 '

Text from CVE List

Affected versions 18

  • Linuxaffected: 1e052be69d045c8d0f82ff1116fd3e5a79661745 before 9e7741b41a25b9d49df4d262fa314342e6f95c50CVE List
  • Linuxaffected: 1e052be69d045c8d0f82ff1116fd3e5a79661745 before 48d38bf8c22a05fde07ba1f885cde27b851649a2CVE List
  • Linuxaffected: 1e052be69d045c8d0f82ff1116fd3e5a79661745 before cc99d26b12431e4e4d0e346ec32764eb42c0aed9CVE List
  • Linuxaffected: 1e052be69d045c8d0f82ff1116fd3e5a79661745 before 41e94079200aaf0cdbe4594b0af75710b33da124CVE List
  • Linuxaffected: 1e052be69d045c8d0f82ff1116fd3e5a79661745 before 2e2f130951d34871b0643bf700164d97cff4b427CVE List
  • Linuxaffected: 1e052be69d045c8d0f82ff1116fd3e5a79661745 before f8495d67434e1cb7e511297687ca55fdb28e4c20CVE List
  • Linuxaffected: 1e052be69d045c8d0f82ff1116fd3e5a79661745 before 81dd117c04422c6d0c7974aba9fa6a0ba370959bCVE List
  • Linuxaffected: 1e052be69d045c8d0f82ff1116fd3e5a79661745 before 1853f30cf5c84971f99788a76207c6f745380896CVE List
  • Linuxaffected: 4.1CVE List
  • Linuxunaffected: all versions before 4.1CVE List
  • Linuxunaffected: 5.10.271 through 5.10.*CVE List
  • Linuxunaffected: 5.15.222 through 5.15.*CVE List
  • Linuxunaffected: 6.1.189 through 6.1.*CVE List
  • Linuxunaffected: 6.6.158 through 6.6.*CVE List
  • Linuxunaffected: 6.12.111 through 6.12.*CVE List
  • Linuxunaffected: 6.18.53 through 6.18.*CVE List
  • Linuxunaffected: 7.2.7 through 7.2.*CVE List
  • Linuxunaffected: 7.3CVE List

References 8