Unexplainable router log entries mentioning IPSEC from Yahoo IPs

techzone at greeleynet.com techzone at greeleynet.com
Sat Dec 19 21:13:36 UTC 2020

Maybe something to do with the shutdown of Yahoo Groups.



Frank Whiteley


From: NANOG <nanog-bounces+techzone=greeleynet.com at nanog.org> On Behalf Of Matthew Petach
Sent: Saturday, December 19, 2020 7:04 AM
To: Dobbins, Roland <Roland.Dobbins at netscout.com>
Cc: NANOG <nanog at nanog.org>
Subject: Re: Unexplainable router log entries mentioning IPSEC from Yahoo IPs



In this case, however, what's being seen is simply valid traffic 

which was most likely erroneously redirected through an 

internal encryption device.


I would hazard a guess the folks involved have already jumped 

on checking the redirector rules to fix the leakage which allowed 

external IPs to be passed through the internal encryption pathway.


I helped build the system that's causing those messages, so I have 

a bit of a guess as to what the issue is.  I'm no longer an employee,

however, so I can't fix the issue.  But in this case, those boxes really 

aren't trying to attack you--they just aren't supposed to be sending 

traffic externally like that.  


So, it actually is good to speak up about this traffic--because it's a fixable 

issue, and one that should be addressed at the source.








On Fri, Dec 18, 2020 at 9:05 PM Dobbins, Roland <Roland.Dobbins at netscout.com <mailto:Roland.Dobbins at netscout.com> > wrote:


On Dec 19, 2020, at 01:19, Frank Bulk <frnkblk at iname.com <mailto: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 <mailto:roland.dobbins at netscout.com> >



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