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CVE-2026-72338
net/sched: act_pedit: fix TOCTOU heap OOB write in tc offload
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem include/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-72338 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
There is a TOCTOU race condition in flower lockless approach between sizing a flow_rule buffer and filling it. zdi-disclosures@trendmicro.com reports: The cls_flower classifier operates with TCF_PROTO_OPS_DOIT_UNLOCKED (fl_change runs without RTNL), while RTM_NEWACTION holds RTNL, so the independent locking domains make the race reachable in practice. KASAN confirms: BUG: KASAN: slab-out-of-bounds in tcf_pedit_offload_act_setup+0x81b/0x930 Write of size 4 at addr ffff888001f27520 by task poc-toctou/312 The buggy address is located 0 bytes to the right of allocated 288-byte region [ffff888001f27400, ffff888001f27520) (cache kmalloc-512) Note: The result is a heap OOB write attacker-controlled content into the adjacent slab object (requires CAP_NET_ADMIN). The fix introduces reading tcfp_nkeys under act->tcfa_lock in all places using a new tcf_pedit_nkeys_locked() which replaces the old tcf_pedit_nkeys(). Additionally we close the remaining TOCTOU window between the sizing read and the fill reads by more careful accounting. Rather than silently truncating the key count, which leads to incorrect action semantics offloaded to hardware and secondary OOB writes if the remaining capacity is zero or consumed by prior actions, we enforce remaining capacity checks and return -ENOSPC if the required space exceeds the remaining capacity.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
include/net/tc_act/tc_pedit.h
net/sched/act_api.c
net/sched/act_pedit.c
net/sched/cls_api.c
- What this is
- TC subsystemMAINTAINERS section matched on include/net/tc_act/ · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_NET_CLS_ACT /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_NET_CLS_ACT
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 5.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- include/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.11 | 6.6.145 | 0d8532a5e972 |
| 4.11 | 6.12.97 | 27488e1a7f19 |
| 4.11 | 6.18.40 | 6f9b23eb92a8 |
| 4.11 | 7.1.5 | 8e49cd891bda |
| 4.11 | 7.2 | 8b519cbcabe8 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bug is reached only through rtnetlink TC APIs (RTM_NEWTFILTER cls_flower offload and RTM_NEWACTION pedit replace), not by processing remote network packets; per kernel guidance tc/qdisc/netlink paths are Local.
- AC:LAttack complexity, low
- This is a TOCTOU race where the attacker runs both sides concurrently (flower filter hardware-offload setup vs RTM_NEWACTION REPLACE increasing pedit keys); Trend Micro reproduced it with task poc-toctou, so timing is attacker-driven not external.
- PR:LPrivileges required, low
- All entry points require CAP_NET_ADMIN (rtnetlink checks netlink_net_capable); that capability is available to an unprivileged user who creates a user+network namespace (unshare -Urn), not only init-namespace root.
- UI:NUser interaction, none
- Exploitation needs no victim interaction; it is triggered entirely by the attacker's concurrent netlink configuration of pedit actions and cls_flower filters.
- S:UScope, unchanged
- Impact is kernel heap corruption and local privilege escalation within the same kernel security domain; it is not a VM escape, hypervisor bypass, or cross-authority sandbox breakout.
- C:HConfidentiality impact, high
- KASAN reports a slab out-of-bounds write of attacker-controlled pedit mangle data into the adjacent kmalloc object; heap corruption of this kind is reasonably leveraged for kernel memory disclosure.
- I:HIntegrity impact, high
- The flaw is a heap out-of-bounds write (KASAN: write of size 4 past a 288-byte region) with attacker-chosen pedit key values, enabling heap grooming and potential control-flow hijack in kernel context.
- A:HAvailability impact, high
- Corrupting adjacent slab objects during tc offload setup can cause immediate kernel oops/panic; KASAN already flags this as slab-out-of-bounds under concurrent offload activity.