Threat ID 411977850 created 2021-06-11 13:58:04 (UTC)

[LeeFrancis2]

We are investigating alerts of this DNS signature for  x1.c.lencr.org.

I'd expect that a match for a clear text string in a DNS Request that it is very unlikely this is a false detection.

However to get alerts so quickly after this signature creation, suggests we are either very unlucky or  a very common public internet resource if causing this fly-by access. Anyone else receiving this threat alert shortly after an apparent WF update.

KR,

Lee

[tehfishman]

Looks like a false positive to me, I can't see why that particular Let'sEncrypt domain is flagged as malicious.

[dlonek]

Did you happen to see additional events to x1.c.lencr.org late last evening until early this morning (12:33am ET to 1:08am ET)?  We saw them the first time during the time you posted in your original post.  

[MBlaylock]

Since the update (2021-06-11) to malware this has caused significant malware alerts. To my knowledge there hasn't been any help desk tickets that parts of the internet isn't working.... Has anyone reached out to #Unit42 for an explanation?

[tehfishman]

Yeah we got bombarded by a few thousand all at once in that timeframe, I have them set to ignore until I see any evidence to suggest that they're something I should actually be concerned about.

[dlonek]

We didn't see thousands but this happened on 6/11 (matching the time frame from the OP), and then last night between between 12:33am and 1:08am ET.  We ran full Bitdefender and Malwarebytes scan, both came back clean.  Hoping this is just a categorization failure on the Palo Threat detections but seems odd it happened twice in 4 days.  

[tehfishman]

I think I see what happened; a bunch of new detections for malware communicating with that letsencrypt domain are now visible in VirusTotal, when they weren't last night. WildFire probably got that data earlier than it was available publicly on VirusTotal. The Let'sEncrypt domain likely isn't malicious, but some malware is pointing to it for some reason (maybe to check validity on a cert? sounds like it might be a cheeky way to do CNC signalling using a public service). That doesn't explain why it has happened twice in 4 days though. Maybe some other data source reported it 4 days ago and they disabled the signature once they realized it wasn't an actionable alert, then re-enabled it when more detections popped up through VT?

https://www.virustotal.com/gui/domain/x1.c.lencr.org/relations

[dlonek]

Certainly possible.  I am concerned if your theory is true.  That would indicate several endpoints have some undetected malware on them.  We fortunately block traffic to this specific endpoint, although only when categorized as malware.  Otherwise I see traffic to this endpoint going back weeks.  We are opening a case with Palo TAC support to better understand what is going on.  If we identify root cause I will provide an update here. 

[Adrian_Jensen]

We have been seeing a spike in alerts for this as well. Logs shows connections to the IPs going back to at least 6/8. Internally, it looks like the DNS requests are being generated from hmpalert.dll on a large number of machines, which is apparently the HitmanPro.Alert service, part of Sophos. We are still investigating.

[askroly1]

I'd be interested to know the root cause if you figure it out.