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VulnerabilityPublished Updated

CVE-2026-68138: Linux kernel · net/sched: serialize qdisc_rtab_list against concurrent get/put

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 7.8 High · fixed in fb29e1b41052488ee3f2d115d4a870497ebd7f7d : patch Linux kernel soon.

Data as of 26 Oct 2026, 12:55 UTC

CVSS 3.1 base score
7.8High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 12% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact
Total control over the software or total information disclosure

CISA SSVC assessment, 2026-10-16.

Patch
Available – fixed in fb29e1b41052488ee3f2d115d4a870497ebd7f7d, f93c89392bd3b180b5b7abc6fdae8e3dd667a313, f43ee0c0730d6191629b5ee1ceae27b1ebfdc047 +5
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 10 Aug 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ 470502de5bdb1ed0def643a4458593a40b8f6b66, < fb29e1b41052488ee3f2d115d4a870497ebd7f7d
Fixed in
  • fb29e1b41052488ee3f2d115d4a870497ebd7f7d
LinuxLinuxAffected
  • ≥ 470502de5bdb1ed0def643a4458593a40b8f6b66, < f93c89392bd3b180b5b7abc6fdae8e3dd667a313
Fixed in
  • f93c89392bd3b180b5b7abc6fdae8e3dd667a313
LinuxLinuxAffected
  • ≥ 470502de5bdb1ed0def643a4458593a40b8f6b66, < f43ee0c0730d6191629b5ee1ceae27b1ebfdc047
Fixed in
  • f43ee0c0730d6191629b5ee1ceae27b1ebfdc047
LinuxLinuxAffected
  • ≥ 470502de5bdb1ed0def643a4458593a40b8f6b66, < d981098b76756ed71666a27518eeb69883657c43
Fixed in
  • d981098b76756ed71666a27518eeb69883657c43
LinuxLinuxAffected
  • ≥ 470502de5bdb1ed0def643a4458593a40b8f6b66, < 4131dd0b6f67acddd616ed7c244e1d3eedd46e7b
Fixed in
  • 4131dd0b6f67acddd616ed7c244e1d3eedd46e7b
LinuxLinuxAffected
  • ≥ 470502de5bdb1ed0def643a4458593a40b8f6b66, < 8ddc2eb0d2da9c83f54f1e5720525b461b8480c4
Fixed in
  • 8ddc2eb0d2da9c83f54f1e5720525b461b8480c4

Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: serialize qdisc_rtab_list against concurrent get/put qdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly linked list qdisc_rtab_list and a plain non-atomic 'int refcnt' with no lock. This was only safe because every caller historically held the RTNL mutex, which serialized all rate-table lookups, inserts and frees. That invariant no longer holds. cls_flower sets TCF_PROTO_OPS_DOIT_UNLOCKED, so tc_new_tfilter() keeps rtnl_held == false for it and sets TCA_ACT_FLAGS_NO_RTNL. That flag propagates through tcf_exts_validate_ex() -> tcf_action_init() -> tcf_action_init_1() -> tcf_police_init(), which calls qdisc_get_rtab()/qdisc_put_rtab() with the RTNL mutex NOT held. Two RTM_NEWTFILTER requests on different CPUs, each adding a flower filter with a police action carrying the same rate, then race on qdisc_rtab_list and on the non-atomic refcnt, leading to a use-after-free / double-free of the kmalloc-2k struct qdisc_rate_table. qdisc_rtab_list is a single global (not per-netns), so the corrupted object is shared system-wide. BUG: KASAN: slab-use-after-free in qdisc_put_rtab+0x12f/0x160 qdisc_put_rtab+0x12f/0x160 tcf_police_init+0xda9/0x1590 tcf_action_init_1+0x460/0x6b0 tcf_action_init+0x439/0xa40 tcf_exts_validate_ex+0x42d/0x550 fl_change+0xddd/0x7da0 tc_new_tfilter+0xaa7/0x2420 rtnetlink_rcv_msg+0x95e/0xe90 which belongs to the cache kmalloc-2k of size 2048 Protect qdisc_rtab_list and the refcount with a dedicated spinlock. The (sleeping, GFP_KERNEL) allocation in qdisc_get_rtab() is performed before taking the lock; if a concurrent inserter added an identical table in the meantime the freshly allocated one is freed under the lock, so no duplicate is leaked. qdisc_put_rtab() now decrements the refcount and unlinks under the same lock.

References

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