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CVE-2026-53212
netfilter: nft_tunnel: fix use-after-free on object destroy
Published 2026-06-25 (4 months ago) by the Linux kernel CNA. Subsystem net/netfilter. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-53212 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 | fixedDLA-4665-1 · 2026-07-03 · text | 6.1.176-1 | Update the kernel and reboot. DLA-4665-1 shipped the fix on 2026-07-03, in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
nft_tunnel_obj_destroy() calls metadata_dst_free() which directly kfree()s the metadata_dst, ignoring the dst_entry refcount. Packets that took a reference via dst_hold() in nft_tunnel_obj_eval() and are still queued (e.g. in a netem qdisc) are left with a dangling pointer. When these packets are eventually dequeued, dst_release() operates on freed memory. Replace metadata_dst_free() with dst_release() so the metadata_dst is freed only after all references are dropped. The dst subsystem already handles metadata_dst cleanup in dst_destroy() when DST_METADATA is set.
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.
net/netfilter/nft_tunnel.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nft_tunnel
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NFT_TUNNEL' /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 nft_tunnelPrints 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_NETFILTER, CONFIG_NFT_TUNNEL
- 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
- 2026-06-25 (4 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
- 0.19%, higher than 8.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/netfilter
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.19 | 5.10.259 | 349df61526d2 |
| 4.19 | 5.15.210 | 55b79b1ae423 |
| 4.19 | 6.1.176 | 5e9ee18b27fd |
| 4.19 | 6.6.143 | 8767fe4079af |
| 4.19 | 6.12.94 | fda6573a46ad |
| 4.19 | 6.18.36 | 941d7394efda |
| 4.19 | 7.0.13 | f9a0e4b61054 |
| 4.19 | 7.1 | c32b26aaa2f9 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4671-1 | 2026-07-05 | bullseye 6.1.176-1~deb11u1 | tracker |
| DLA-4665-1 | 2026-07-03 | bookworm 6.1.176-1 | tracker |
| DLA-4664-1 | 2026-07-03 | bullseye 5.10.259-1 | tracker |
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 vulnerable nft_tunnel object is created, referenced, and destroyed through nf_tables netlink operations and packet processing configured locally via nftables/netdev hooks. Remote packets may help populate a queue, but exploitation requires local control of nftables transactions.
- AC:LAttack complexity, low
- The attacker can set up the tunnel object/rule, arrange queued packets such as with netem, and delete the rule/object sequence under their control. No uncontrollable race or rare external condition is required.
- PR:LPrivileges required, low
- nfnetlink requires CAP_NET_ADMIN in the socket network namespace, and nftables/netfilter is reachable by an unprivileged local user through user and network namespaces on typical affected systems. This is low privilege rather than real init-namespace root.
- UI:NUser interaction, none
- No victim user action is required after the attacker has local execution. The trigger is performed through attacker-issued netlink configuration and packet generation/dequeue.
- S:UScope, unchanged
- The bug corrupts kernel networking memory and can lead to local kernel privilege escalation within the same security authority. It is not a VM escape, IOMMU bypass, or other CVSS scope-changing boundary crossing.
- C:HConfidentiality impact, high
- This is a heap use-after-free of a metadata_dst referenced from queued skbs, and similar nf_tables UAFs are exploitable for kernel memory disclosure. Following the higher-severity rule for UAFs, confidentiality impact is high.
- I:HIntegrity impact, high
- The freed dst/metadata object can be reclaimed and later operated on through dst_release and related networking paths, giving a plausible route to memory corruption and control-flow or arbitrary write exploitation. Following the kernel UAF guidance, integrity impact is high.
- A:HAvailability impact, high
- Even without full exploitation, dequeuing packets with a dangling dst pointer can cause a kernel oops, panic, or memory-corruption crash. Availability impact is therefore high.