CVE-2026-80634
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk5th percentile - higher than 5% of all known CVEs
Summary
In the Linux kernel, the netfilter flowtable module has an underflow of num_encaps when untagging VLAN on a bridge, which can lead to an out-of-bounds stack read. This only happens with a malformed bridge path stack.
Risk Assessment
This can lead to system crashes or incorrect routing behavior under specific conditions.
Recommendation
Install a kernel patch that moves the decrement out of WARN_ON_ONCE and removes that warning.
Original NVD description (English source)
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 ].