In the Linux kernel, the following vulnerability has been resolved: netfilter: nftobjref: 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: _findrrleaf+0x99/0x230 fib6tablelookup+0x13b/0x2d0 ip6polroute+0xa4/0x400 fib6rulelookup+0x156/0x240 ip6routeoutputflags+0xc6/0x150 _nfip6route+0x23/0x50 synproxysendtcpipv6+0x106/0x200 synproxysendclientsynackipv6+0x1aa/0x1f0 nftsynproxydoeval+0x263/0x310 nftdochain+0x5a8/0x5f0 [nftables nftdochaininet+0x98/0x110 nfhookslow+0x43/0xc0 _ip6localout+0xf0/0x170 ip6localout+0x17/0x70 synproxysendtcpipv6+0x1a2/0x200 synproxysendclientsynackipv6+0x1aa/0x1f0 [...] Implement objref and objrefmap expression validate functions. Currently, only NFTOBJECTSYNPROXY 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 ^^^^^^^^^^^^^^^^^^^^^^^^