# CVE-2026-68138: net/sched: serialize qdisc_rtab_list against concurrent get/put

> A race condition in the Linux kernel's network scheduler allows local attackers to trigger a use-after-free, potentially leading to privilege escalation or code execution.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Aug 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-95012, BELL-CVE-2026-68138, DEBIAN-CVE-2026-68138, GHSA-5w39-288f-6m96, UBUNTU-CVE-2026-68138

## What is CVE-2026-68138?

CVE-2026-68138 is a high-severity vulnerability in Linux, published on 10 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-68138?


## How do I fix CVE-2026-68138?

Apply the vendor's patch.

## Is CVE-2026-68138 being exploited?

There is no known exploitation of CVE-2026-68138 in the wild and no public exploit code.

Public exploit code:

- CVE-2026-68138 Linux qdisc rate-table race local privilege escalation PoC (github_poc): https://github.com/aramosf/CVE-2026-68138
- Tracking CVE-2026-68138, the Linux kernel net/sched qdisc rate-table use-after-free (github_poc): https://github.com/suominen/CVE-2026-68138
- CVE-2026-68138 Linux Local Privilege Escalation Exploit (github_poc): https://github.com/jangkrikkbozz/CVE-2026-68138

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68138 and fix it if it is affected.

What it is: CVE-2026-68138 is a high-severity vulnerability in Linux, published on 10 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-68138 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-68138/ (Markdown: https://insights.sbomify.com/CVE-2026-68138/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68138
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68138
- OSV: https://osv.dev/vulnerability/CVE-2026-68138

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68138/
Summaries are generated and may contain mistakes; the official description above is the record.