Unexplainable router log entries mentioning IPSEC from Yahoo IPs

Dobbins, Roland Roland.Dobbins at netscout.com
Sat Dec 19 05:02:48 UTC 2020

On Dec 19, 2020, at 01:19, Frank Bulk <frnkblk at iname.com> wrote:

Curious if someone can point me in the right direction. In the last three
days our core router (Cisco 7609) has logged the following events:

Dec 16 19:04:59.027 CST: %CRYPTO-4-RECVD_PKT_INV_SPI: decaps: rec'd IPSEC
packet has invalid spi for destaddr=<redacted>, prot=50,
spi=0xEF7ED795(4018067349), srcaddr=, input interface=Vlan20

It should be noted that attackers will sometimes generate non-TCP/-UDP/-ICMP DDoS attack traffic which is intended to bypass ACLs, firewall rules, etc. which only take the more common protocols into account. They'll often pick ESP (protocol 50, AH (protocol 51), or GRE (protocol 47) in order to try & masquerade the attack traffic as legitimate VPN or tunneled traffic.

And the source IPs of this attack traffic are frequently spoofed, as well.


Roland Dobbins <roland.dobbins at netscout.com>

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