observation: masses of requests to LDAP

observation: masses of requests to LDAP

[Tobias Wendorff]

Hi there,

our IT department has informed me that masses of requests are being sent 
from my computer to our two LDAP servers on port 389. After a detailed 
investigation, the problem could be clearly traced back to "cygwin".

Firewall logs show that about any tool, even base tools "sort" or 
"less", initiates a request to port 389 on our LDAP servers.

Sorry, I am _not_ going to release "cygcheck.out" to public, since it 
contains sensitive information about the domain and its groups and 
memberships.

Even after reinstalling cygwin from another server, the problem still 
appears. Could it be that this is part of an attack?

Best regards,
Tobias

Re: observation: masses of requests to LDAP

[Brian Inglis]

On 2023-01-22 07:32, Tobias Wendorff via Cygwin wrote:
> our IT department has informed me that masses of requests are being sent from my 
> computer to our two LDAP servers on port 389. After a detailed investigation, 
> the problem could be clearly traced back to "cygwin".

That is required for Cygwin to emulate POSIX permissions and ACLs: see security 
and domain info in:

/usr/share/doc/cygwin-doc/html/cygwin-ug-net/cygwin-ug-net.html
/usr/share/doc/cygwin-doc/cygwin-ug-net.pdf

or the equivalant online docs:

https://cygwin.com/cygwin-ug-net.html
https://cygwin.com/cygwin-ug-net/cygwin-ug-net.html
https://cygwin.com/cygwin-ug-net/cygwin-ug-net.pdf
https://cygwin.com/faq.html

Your IT folks could contact peers at Aachen, Bochum, Dresden, Esslingen, FAU who 
provide Cygwin mirrors, probably use it in courses, and have experience with it; 
see:
	https://cygwin.com/mirrors.html

> Firewall logs show that about any tool, even base tools "sort" or "less", 
> initiates a request to port 389 on our LDAP servers.

Each process needs access to your credentials, groups, and memberships, and 
pulls them for domain accounts on domain members.

> Sorry, I am _not_ going to release "cygcheck.out" to public, since it contains 
> sensitive information about the domain and its groups and memberships.

It is acceptable to anonymize or summarize information in cygcheck output.
In this case, counts of ids, groups, and memberships might help.

> Even after reinstalling cygwin from another server, the problem still appears. 
> Could it be that this is part of an attack?

Definitely not, this is normal behaviour.

Your first step should be to run cygserver to cache SAM and AD info on each 
system using cygwin on domain members.

Your second step should be to review /etc/nsswitch.conf settings for searching 
and possibly set:

	db_enum: cache local primary builtin

or maybe:

	db_enum: cache local primary alltrusted

or if connecting from home maybe:

	db_enum: cache local primary domain.tld

Check the mainling list archives for previous posts about domain settings.

-- 
Take care. Thanks, Brian Inglis			Calgary, Alberta, Canada

La perfection est atteinte			Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter	not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer	but when there is no more to cut
			-- Antoine de Saint-Exupéry

Re: observation: masses of requests to LDAP

[Corinna Vinschen]

On Jan 22 15:32, Tobias Wendorff via Cygwin wrote:
> Hi there,
> 
> our IT department has informed me that masses of requests are being sent
> from my computer to our two LDAP servers on port 389. After a detailed
> investigation, the problem could be clearly traced back to "cygwin".
> 
> Firewall logs show that about any tool, even base tools "sort" or "less",
> initiates a request to port 389 on our LDAP servers.
> 
> Sorry, I am _not_ going to release "cygcheck.out" to public, since it
> contains sensitive information about the domain and its groups and
> memberships.
> 
> Even after reinstalling cygwin from another server, the problem still
> appears. Could it be that this is part of an attack?

No, it's working as designed.  User info is fetched from AD via LDAP.
If it's an overwhemling number of LDAP requests, I suspect you're
often calling Cygwin processes from Windows directly, e. g., from
CMD or powershell.  The number of LDAP requests should be much
reduced when working from a Cygwin shell, e.g., from bash in mintty
due to user and group info cashing within a Cygwin process tree
(Cygwin child processes get the cashed info from their Cygwin parent).

If you want to reduce LDAP access even further, you can either
go back to creating local /etc/passwd and /etc/group files and
change /etc/nsswitch.conf accordingly(*), or you can start cygserver
as a service in background(**).


HTH,
Corinna

(*)  https://cygwin.com/cygwin-ug-net/ntsec.html#ntsec-mapping-nsswitch
(**) https://cygwin.com/cygwin-ug-net/ntsec.html#ntsec-mapping-caching