My relays have been patched to the latest available kernels, and aren't in the list of vulnerable relays, however they still show high values for TCPSYNChallenge:

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$ ansible tor -a 'bash -c "netstat -s | grep -i challenge"' -b --ask-become-pass

lon | SUCCESS | rc=0 >>

    TCPChallengeACK: 14197

    TCPSYNChallenge: 2926

fra | SUCCESS | rc=0 >>

    TCPChallengeACK: 12907

    TCPSYNChallenge: 3461

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$ ansible tor -a 'bash -c "cat /etc/lsb-release && uname -rv"' -b --ask-become-pass

fra | SUCCESS | rc=0 >>

DISTRIB_ID=Ubuntu

DISTRIB_RELEASE=14.04

DISTRIB_CODENAME=trusty

DISTRIB_DESCRIPTION="Ubuntu 14.04.5 LTS"

3.13.0-101-generic #148-Ubuntu SMP Thu Oct 20 22:08:32 UTC 2016

lon | SUCCESS | rc=0 >>

DISTRIB_ID=Ubuntu

DISTRIB_RELEASE=14.04

DISTRIB_CODENAME=trusty

DISTRIB_DESCRIPTION="Ubuntu 14.04.5 LTS"

3.13.0-101-generic #148-Ubuntu SMP Thu Oct 20 22:08:32 UTC 2016

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