Look up another CVE · open CVE-2026-80634 in the interactive tracker
CVE-2026-80634
netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag
Published 2026-08-28 (2 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-2026-80634 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 | 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
The DEV_PATH_BR_VLAN_UNTAG case post-decrements info->num_encaps inside WARN_ON_ONCE(). num_encaps is u8, so if it's already 0 the decrement still happens and wraps it to 255. The break only leaves the inner switch -- a later path entry can set info->indev back to a real device, and we end up returning with num_encaps == 255. nft_dev_forward_path() then walks info.encap[] (size 2) up to num_encaps, which means an OOB stack read and a bogus count copied into the route descriptor. Should only happen on a malformed bridge path stack, hence the WARN, but worth handling sanely. Move the decrement out of the WARN. [ While at this, remove the WARN_ON_ONCE since this can only happen with a buggy bridge path stack --pablo ].
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/nf_flow_table_path.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nf_flow_table
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NF_FLOW_TABLE' /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 nf_flow_tablePrints 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 with an answer 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. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidm
- ?
- not established - no Makefile entry for the affected file
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
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 switches
- CONFIG_NETFILTER, CONFIG_NF_FLOW_TABLE
- 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
- 2026-08-28 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.65%, higher than 50.1% 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 |
|---|---|---|
| 5.13 | 6.18.57 | 547ea9f56749 |
| 5.13 | 7.1.5 | 2f55fa28011c |
| 5.13 | 7.2 | e052f920773b |
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:NAttack vector, network
- The bug is hit in nft_flow_offload_eval on NF_INET_FORWARD when remotely sourced TCP/UDP packets matching a conntrack flow trigger nft_flow_route() and nft_dev_forward_path() during softirq packet processing on nftables flowtable routers/gateways, not via netlink configuration APIs.
- AC:LAttack complexity, low
- Once an nftables flowtable with bridge VLAN filtering is deployed, an attacker can establish confirmed TCP/UDP flows and steer traffic through the affected bridge/VLAN topology to reach nft_dev_path_info() without races or other conditions outside the attacker's control.
- PR:NPrivileges required, none
- Flowtable and bridge VLAN setup are administrator deployment prerequisites; a remote sender needs no local account, authentication, or CAP_NET_ADMIN on the victim to trigger flow offload path resolution while forwarding traffic through the configured bridge.
- UI:NUser interaction, none
- Exploitation requires only sending network packets processed automatically on the forwarding path; no victim must open files, mount filesystems, or take any interactive action beyond normal traffic through the router.
- S:UScope, unchanged
- Out-of-bounds stack reads and writes in nft_dev_forward_path() corrupt kernel stack memory and route descriptors on the affected host only; this is standard kernel compromise within one security authority, not a VM escape or cross-boundary sandbox break.
- C:HConfidentiality impact, high
- When num_encaps underflows to 255, nft_dev_forward_path() loops up to 255 times over info.encap[2], performing out-of-bounds stack reads of adjacent kernel stack memory that can disclose pointers and other sensitive data.
- I:HIntegrity impact, high
- The same loop writes attacker-influenced encap values past route->tuple[].in.encap[2] on the stack, corrupting adjacent route fields and stack data in ways that can be leveraged for arbitrary kernel writes and control-flow hijack.
- A:HAvailability impact, high
- Massive out-of-bounds stack corruption during flow offload setup in softirq context can cause immediate kernel oops/panic and reliable denial of service on forwarding routers processing malicious traffic through vulnerable bridge VLAN paths.