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CVE-2026-43042
mpls: add seqcount to protect the platform_label{,s} pair
Published 2026-05-01 (6 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-2026-43042 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 | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| Debian 14forky | fixed | 6.19.12-1 | Update the kernel and reboot. Fixed in 6.19.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.19.12-1 | Update the kernel and reboot. Fixed in 6.19.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The RCU-protected codepaths (mpls_forward, mpls_dump_routes) can have an inconsistent view of platform_labels vs platform_label in case of a concurrent resize (resize_platform_label_table, under platform_mutex). This can lead to OOB accesses. This patch adds a seqcount, so that we get a consistent snapshot. Note that mpls_label_ok is also susceptible to this, so the check against RTA_DST in rtm_to_route_config, done outside platform_mutex, is not sufficient. This value gets passed to mpls_label_ok once more in both mpls_route_add and mpls_route_del, so there is no issue, but that additional check must not be removed.
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/netns/mpls.h
net/mpls/af_mpls.c
- What this is
- NETWORKING [GENERAL]MAINTAINERS section matched on include/net/ · netdev@vger.kernel.org · Maintained
- Kernel module
- mpls_router
Check it on the machine
grep -wE 'CONFIG_MPLS|CONFIG_MPLS_ROUTING' /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.
lsmod | grep -w mpls_routerPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_MPLS, CONFIG_MPLS_ROUTING
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-05-01 (6 months ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.16%, higher than 4.3% 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 |
|---|---|---|
| 4.1 | 6.19.12 | 5bb3caf0bbfb |
| 4.1 | 7.0 | 629ec78ef860 |
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 self-contained exploit path is local: the attacker races writes to /proc/sys/net/mpls/platform_labels with rtnetlink RTM_GETROUTE dumps in the same network namespace. Remote MPLS packets can reach one reader path, but a remote-only attacker cannot perform the required table resize.
- AC:LAttack complexity, low
- The vulnerable condition is a race, but a local attacker can control both sides by repeatedly resizing platform_labels and issuing concurrent route dumps or packet processing. No external timing or victim state is required beyond retrying the race.
- PR:LPrivileges required, low
- Writing the MPLS platform_labels sysctl requires CAP_NET_ADMIN over the target network namespace. That capability is reachable by an unprivileged user through a user namespace plus network namespace, so this is low privilege rather than high privilege.
- UI:NUser interaction, none
- No victim user action is required. The attacker can trigger the resize and reader paths directly.
- S:UScope, unchanged
- The bug is within the kernel networking/MPLS subsystem and impacts the same kernel security authority. It is not a VM escape or cross-authority boundary bypass.
- C:HConfidentiality impact, high
- The inconsistent platform_labels/platform_label snapshot can cause out-of-bounds reads of the route pointer table and dereference attacker-influenced or adjacent kernel memory as mpls_route data. Through the route dump path this can disclose kernel memory, so confidentiality is high.
- I:NIntegrity impact, none
- The bug is an out-of-bounds read/dereference of the route table pointer array, not an out-of-bounds write or direct memory corruption primitive. The investigated paths do not provide a defensible arbitrary kernel data modification primitive.
- A:HAvailability impact, high
- The race can make readers index a NULL, stale, or too-small platform_label array and dereference invalid pointers. This can reliably lead to kernel oops/panic or other high availability impact.