On Tue, 13 Aug 2024, David Lang wrote:
by default, ethernet packets are limited to 1500 bytes, most OSs will
fragment UDP messages >1500 bytes across multiple packets. As I noted before,
this means that if one of the packets of a message get lost, the entore
message is lost
Rsyslog supports this, but it sounds like something else in your environment
is not allowing it.
the fact that you are seeing the messages via tcpdump still confuses me. But
I'm glad you got things working
going back and looking at the tcpdump you provided, that's the 1st 1500 byte
packet of the message, if the 2nd fragment is getting dropped by the OS
(possible, fragment assembly is a common way to bypass firewall filters, so
blocking additional packets that claim to be fragments of a message you already
received is a valid security thing to do if you don't need longer UDP messages)
and as such, rsyslog would never see them
note that you can increase the MTU to up to 9000 bytes (search for jumbo
packets) if everything on your network supports it, and you will handle larger
messages and in general your network will be more efficient.
David Lang
David Lang
On Tue, 13 Aug 2024, Drumm, Daniel wrote:
Date: Tue, 13 Aug 2024 23:19:42 +0000
From: "Drumm, Daniel" <daniel.dr...@dob.texas.gov>
To: David Lang <da...@lang.hm>
Cc: rsyslog-users <rsyslog@lists.adiscon.com>
Subject: RE: [rsyslog] Formatting CEF to log.
David -
After experimenting and speaking with a Microsoft engineer, the underlying
issue is known to Microsoft. Rsyslog will truncate or drop long messages in
CEF format unless TCP is used. UDP cannot be used. This was in a side note
in their documentation I missed, early docs made it appear as they were
agnostic about the syslog transport, but this is not the case.
Once I did this, and altered rsyslog.conf to listen with tcp:
# /etc/rsyslog.conf configuration file for rsyslog
#
# For more information install rsyslog-doc and see
# /usr/share/doc/rsyslog-doc/html/configuration/index.html
#
# Default logging rules can be found in /etc/rsyslog.d/50-default.conf
#################
#### MODULES ####
#################
module(load="imudp") # needs to be done just once
input(type="imudp" port="514")
module(load="imtcp") # load TCP listener
input(type="imtcp" port="514") # start TCP listener on port 514
$ModLoad imuxsock # needs to be done just once
# $AllowedSender - specifies which remote systems are allowed to send
syslog messages to rsyslogd
# --------------
$AllowedSender TCP, UDP, 127.0.0.1, 10.40.0.0/16, 10.30.0.0/23
$SystemLogSocketFlowControl on # enable flow control (use if needed)
$ActionFileEnableSync off
... and so on...
Then, I would see the entirety of the CEF message when that format was sent
in the log files. TCP had to be used.
2024-08-13 23:14:38 DOB-FW-HA-1.OCI Ashburn FD1 CEF:0|Palo Alto
Networks|PAN-OS|11.2.0|end|TRAFFIC|1|rt=Aug 13 2024 23:14:43 GMT
deviceExternalId=007959000479054 src=178.128.104.233 dst=10.40.1.97
sourceTranslatedAddress=178.128.104.233
destinationTranslatedAddress=10.50.0.166 cs1Label=Rule cs1=Inbound to
Untrust NAT Mapping suser= duser= app=web-browsing cs3Label=Virtual System
cs3=vsys1 cs4Label=Source Zone cs4=Untrust cs5Label=Destination Zone
cs5=Trust deviceInboundInterface=ethernet1/2
deviceOutboundInterface=ethernet1/1 cs6Label=LogProfile cs6=OCI Syslog
Server Profile cn1Label=SessionID cn1=129748 cnt=1 spt=52452 dpt=443
sourceTranslatedPort=52452 destinationTranslatedPort=443
flexString1Label=Flags flexString1=0x1400010 proto=tcp act=allow
flexNumber1Label=Total bytes flexNumber1=4857 in=997 out=3860
cn2Label=Packets cn2=14 PanOSPacketsReceived=5 PanOSPacketsSent=9 start=Aug
13 2024 23:14:43 GMT cn3Label=Elapsed time in seconds cn3=1 cs2Label=URL
Category cs2=any externalId
=7392297676068849671 reason=threat PanOSDGl1=0 PanOSDGl2=0 PanOSDGl3=0
PanOSDGl4=0 PanOSVsysName= dvchost=DOB-FW-HA-1 cat=from-policy
PanOSActionFlags=0x0 PanOSSrcUUID= PanOSDstUUID= PanOSTunnelID=0
PanOSMonitorTag= PanOSParentSessionID=0 PanOSParentStartTime=
PanOSTunnelType=N/A PanOSSCTPAssocID=0 PanOSSCTPChunks=0 PanOSSCTPChunkSent=0
PanOSSCTPChunksRcv=0 PanOSRuleUUID=940d959b-9f14-4032-acc5-5a59fa146d4b
PanOSHTTP2Con=0 PanLinkChange=0 PanPolicyID= PanLinkDetail= PanSDWANCluster=
PanSDWANDevice= PanSDWANClustype= PanSDWANSite= PanDynamicUsrgrp= PanXFFIP=
PanSrcDeviceCat= PanSrcDeviceProf= PanSrcDeviceModel= PanSrcDeviceVendor=
PanSrcDeviceOS= PanSrcDeviceOSv= PanSrcHostname= PanSrcMac= PanDstDeviceCat=
PanDstDeviceProf= PanDstDeviceModel= PanDstDeviceVendor= PanDstDeviceOS=
PanDstDeviceOSv= PanDstHostname= PanDstMac= PanContainerName=
PanPODNamespace= PanPODName= PanSrcEDL= PanDstEDL= PanGPHostID= PanEPSerial=
PanSrcDAG= PanDstDAG= PanHASessionOwner= PanTimeHighRes=2024-08-13T18:
14:44.446-05:00 PanASServiceType= PanASServiceDiff=
-----Original Message-----
From: David Lang <da...@lang.hm>
Sent: Tuesday, August 13, 2024 3:43 PM
To: David Lang <da...@lang.hm>
Cc: Drumm, Daniel <daniel.dr...@dob.texas.gov>; rsyslog-users
<rsyslog@lists.adiscon.com>
Subject: RE: [rsyslog] Formatting CEF to log.
I will also point out that templates in rsyslog are for output only, they
have no effect at all on parsing input.
David Lang
On Tue, 13 Aug 2024, David Lang wrote:
Date: Tue, 13 Aug 2024 13:42:38 -0700 (PDT)
From: David Lang <da...@lang.hm>
To: "Drumm, Daniel" <daniel.dr...@dob.texas.gov>
Cc: David Lang <da...@lang.hm>, rsyslog-users
<rsyslog@lists.adiscon.com>
Subject: RE: [rsyslog] Formatting CEF to log.
Drumm, Daniel wrote:
David -
If you want me to instance a brand-new Ubuntu 22.04 VM in the cloud,
get rsyslog on it, and move the 514/udp Palo flow to it, I can do that.
Conversely, if you have access to a PAN-OS instance or old physical
firewall, page 8-10 of this guide will set the CEF parameters and, if
I am guessing correctly, will cause rsyslogd not to log the messages
anywhere even with a *.* directive.
https://gcc02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoc
s.paloaltonetworks.com%2Fcontent%2Fdam%2Ftechdocs%2Fen_US%2Fpdf%2Fcef
%2Fpan-os-10-0-cef-configuration-guide.pdf&data=05%7C02%7CDaniel.Drum
m%40dob.texas.gov%7Cd9cb543b675741ac397e08dcbbd89612%7C32a53eeb27594e
f4af2858fd990c7d67%7C1%7C0%7C638591786114830361%7CUnknown%7CTWFpbGZsb
3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D
%7C0%7C%7C%7C&sdata=fvo7n1H%2Bpm2q1BY4vG2sTRGRP7oGGSCSGuI00k9tYnU%3D&
reserved=0
If, as you state, the behavior of rsyslog is best effort to write to
log even if the fields are misaligned, then I cannot explain the
behavior I see. Per the discussion on tcpdump, I do not believe these
UDP packets to be corrupt or excessively fragmented beyond the MSS. I
cannot explain why the basic *.* is not logging the messages when the
CEF formatting is applied to the firewall. Again, looking at the
packets using tcpdump -v, I know they are arriving, and are about 50%
longer than the base log messages.
it's beyond that, rsyslog does not parse the fields out of the log as
it receives them.
I don't have a pan firewall handy, so please run this test and show
the results.
David Lang
Daniel Drumm, CISSP
Information Security Officer
Texas Department of Banking
512-475-1328
daniel.dr...@dob.texas.gov
-----Original Message-----
From: David Lang <da...@lang.hm>
Sent: Tuesday, August 13, 2024 2:20 PM
To: Drumm, Daniel <daniel.dr...@dob.texas.gov>
Cc: David Lang <da...@lang.hm>; rsyslog-users
<rsyslog@lists.adiscon.com>
Subject: RE: [rsyslog] Formatting CEF to log.
Drumm, Daniel wrote:
Is there a rsyslog Template that exists to take the data in this
format and log it? As you state, when rsyslogd gets a malformed
message, or one with fields additional to that it understands or
knows, it will not log it at all, will not write it to disk at all,
not even a partial malformed log.
No, that is the opposite of what I stated.
When Rsyslog recieves a message, it attempts to parse the timestamp,
fromhost, and syslog tag out of it, and everything else is the string
'msg'. If the log is not properly formatted, it may put the wrong
things in these fields, but it will put SOMETHING there (best effort)
It also populates the filed 'rawmsg' with whatever arrived.
it does not care if the msg field is CEF:whatever or 'the quick brown
fox...'
you can then parse fields out of the message if you care to, but the
msg and rawmsg fields will be there no matter what.
If the message is longer than your configured maxmessagelength, you
will get a log message that is truncated at that length (and then,
depending on the config, either throw away the rest of the message,
or split it at that point into a second, malformed message containing
the next maxmessagelength characters that are sent)
but it will not just throw them away because it doesn't understand them.
I have seen the OS IP stack throw away UDP messages when they are
extremely long and get fragmented into multiple packets and some of
the packets never arrive due to congestion problems on the network,
but that is an intermittent problem, you would have some get through
and others not (and it's been a long time since I saw this because
networks are now much faster than they used to be, so it's far less
common for a network to be that congested, but is still possible)
but the fact that you are seeing them via tcpdump would make it
unlikely that this is the problem.
Can you setup a test where the Palo Alto is only sending the traffic
messages to a test machine and setup a very trivial rsyslog config
just writing it to a file? we may end up wanting to get a debug log
if it still fails there.
David Lang
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