netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag
CVE-2026-80634 · published 28 Aug 2026
How serious is it
- Severity: critical, CVSS score 9.8 out of 10.
- No exploit prediction (EPSS) score yet.
- Not on the CISA list of exploited vulnerabilities.
- No public exploit in Exploit-DB.
Is your app affected by CVE-2026-80634?
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Who is affected
- Linux Linux: e990cef6516daa4e1e236433579e333f74fd38cb to < 1b52aeb40c9f04bf50eeb4ea09142139d163e239, e990cef6516daa4e1e236433579e333f74fd38cb to < ee8440bb000fff4ef8acbfc99652851e9ca0a35b, e990cef6516daa4e1e236433579e333f74fd38cb to < 547ea9f567498e4accc89e7816264f15a1a0629f, e990cef6516daa4e1e236433579e333f74fd38cb to < 2f55fa28011c97d6495d5787808db10a8c2d690d
- Linux Linux: 5.13
How to check
- Find out whether you run the affected product and which version, then compare it with the versions above.
How to fix
Copies a prompt for Claude Code, Cursor or Codex that asks it to check whether you run this product.
- Apply the vendor's update or mitigation from the references below. If there is none yet, limit exposure of the affected service until there is.
- If a vulnerable version was live, check your logs and rotate the secrets that server could read.
The advisory
In the Linux kernel, the following vulnerability has been resolved:
netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag
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 ].
Check your whole app
Dependencies are only half of it. Free and read-only: before you push, run npx shippable-dev scan localhost:3000 in your project folder, no account needed. For your live app, you prove it's yours with a one-line tag first.
References
- git.kernel.org/stable/c/1b52aeb40c9f04bf50eeb4ea09142139d163e239
- git.kernel.org/stable/c/ee8440bb000fff4ef8acbfc99652851e9ca0a35b
- git.kernel.org/stable/c/547ea9f567498e4accc89e7816264f15a1a0629f
- git.kernel.org/stable/c/2f55fa28011c97d6495d5787808db10a8c2d690d
- git.kernel.org/stable/c/e052f920773b73be49eb4d8702a9f85de7464363
Merged from CVE List. Last updated 26 Oct 2026. All vulnerabilities · RSS · JSON