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CVE-2026-64027
net: shaper: rework the VALID marking (again)
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem include/net. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-64027 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Recent commit changed the semantics from NOT_VALID to VALID. I didn't realize that the flags are not stored atomically with the entry in XArray. There's still a race of reader observing a VALID mark for a slot, getting interrupted, writer replacing the entry with a different one, reader continuing, fetching the entry which is now a different pointer than the pointer for which VALID was meant. The biggest consequence of this is that we may see a UAF since net_shaper_rollback() assumed that entries without VALID can be freed without observing RCU. Looks like the XArray marks are buying us nothing at this point. Let's convert the code to an explicit valid field. The smp_load_acquire() / smp_store_release() barriers are marginally cleaner.
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/net_shaper.h
net/shaper/shaper.c
- What this is
- NETWORKING [GENERAL]MAINTAINERS section matched on include/net/ · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_NET_SHAPER /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 with an answer below compiles the affected file into the kernels it ships. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidy
- ?
- not established - no Makefile entry for the affected file
- y
- built into the kernel image on every flavour - only a patch removes it
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switch
- CONFIG_NET_SHAPER
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
- 2026-07-19 (3 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
- 0.13%, higher than 2.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.13 | 6.18.34 | 2417df5e7bb4 |
| 6.13 | 7.0.11 | 96ea960dd40f |
| 6.13 | 7.1 | b8d7519352ba |
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 vulnerability is reached only through the net-shaper generic netlink API (socket syscall), not via remote packet handling. This matches the kernel guidance for tc/netlink-style configuration subsystems.
- AC:LAttack complexity, low
- The family sets parallel_ops, so an attacker can run concurrent SET/GROUP/DELETE and GET/dump requests to control both sides of the TOCTOU race. No attacker-uncontrollable memory layout or rare timing is required beyond issuing concurrent netlink operations.
- PR:LPrivileges required, low
- Exploitation requires triggering net_shaper_rollback() via SET, GROUP, or DELETE, which are gated by GENL_ADMIN_PERM (CAP_NET_ADMIN). That capability is available to an unprivileged user inside a user network namespace, not only to init-namespace root.
- UI:NUser interaction, none
- Exploitation is fully programmatic through netlink messages and requires no victim interaction such as mounting a filesystem or opening a file.
- S:UScope, unchanged
- Impact is kernel heap corruption and privilege escalation within the same kernel; it does not cross a VM, container runtime, or IOMMU security boundary by itself.
- C:HConfidentiality impact, high
- The commit explicitly identifies a use-after-free; concurrent RCU readers can dereference freed net_shaper objects, enabling arbitrary kernel memory disclosure via UAF exploitation.
- I:HIntegrity impact, high
- UAF on heap-allocated net_shaper structures can be leveraged for heap grooming and arbitrary write or control-flow hijack, consistent with standard kernel UAF impact.
- A:HAvailability impact, high
- The UAF can cause kernel oops or panic on freed-object access during lookup, dump, or rollback, and matches kernel guidance that any UAF warrants High availability impact.