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 ].
Advisories

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Fixes

Solution

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Workaround

No workaround given by the vendor.

History

Fri, 28 Aug 2026 11:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-125

Fri, 28 Aug 2026 07:30:00 +0000

Type Values Removed Values Added
Description 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 ].
Title netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

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cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-08-28T06:48:49.022Z

Reserved: 2026-08-26T14:34:25.777Z

Link: CVE-2026-80634

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-08-28T08:16:48.303

Modified: 2026-08-28T08:16:48.303

Link: CVE-2026-80634

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-28T12:15:04Z

Weaknesses