High · published November 13, 2025
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
^^^^^^^^^^^^^^^^^^^^^^^^