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SAP Message Server research presented at OPCDE 2019
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README.md

SAP Message Server research

Copyright (c) 2018-2019 by Mathieu Geli, Dmitry Chastuhin

Proof of concept code for two new attacks on the SAP Message Server component:

  • Logon Group (transparent) Hijacking : sap_ms_dispatcher_mitm.py
  • BeTrusted: sap_ms_betrusted.py

with an utility for SAP MS storage monitoring.

Presentation

OPCDE 2019 Dubai:

The slides of the presentation are available here

Threat analysis

Recent news coverage can be misleading for non SAP-savvy IT responsible and is missing some threat analysis on our publication.

Gateway issue

This is issue is known publicly since 2007, and securing guidelines were published by SAP since 2009. From our experience this issue has mostly disappeared as servers are updated, and old one are being secured.

When the issue is present, with the code released by my ex-colleague Dmitry Chastuhin here, it is possible to run OS commands on the remote server via anonymous network access.

In order to get access to business data, the attacker need to have specific SAP internals knowledge. A script kiddie/automated tool will barely launch a cryptocurrency miner.

Message Server issue

This is the enabler for bypassing the secure Gateway configuration.

The issue relies on the Message Server ACL file that is too open (HOST=*) by default. SAP first published in 2005 guideline on building secure ACL files (basically writing your AS names instead of *).

Published PoC sap_ms_betrusted.py is not reliable and highly dependant on SAP kernel version. It means success is not ensured even if the proper version is implemented. Having something stable will require a good amount of SAP and reverse engineering expertise.

As we explained in our presentation, lab testing was done using full SAP server as the attacker's host, so an attacker do not need our python script to gain successful exploitation.

Exploitation detection

Those measures allow to track sign of exploitation.

Gateway activity

  • Monitor gateway access and transactions executed: SAPXPG is the transaction program to look for, used in our SAPanonGW PoC to run OS command. Gateway developer logs are stored in the dev_rd file and application logs can be configured via transaction SMGW.
  • Network traffic analysis for discovering untrusted sources connecting to gateway port (tcp/33NN)

Security firms already published signatures to detect this specific attack. As any signature-based measure it could be bypassed and should not be taken as a silver bullet for detection, but still is better than nothing.

Message server activity

  • The dev_ms developer log file stores connection information on the Message Server
  • You can have a real-time view by using transaction SMMS via SAP GUI
  • Network traffic analysis for discovering untrusted sources connecting to the Message Server internal port tcp/39NN

As for the gateway, NIDS signatures could be built by matching the string _SEND_NILIST with:

  • src host: SAP server
  • src port: 39NN
  • dest host: not SAP server VLAN

Remediation

Gateway

  • Secure your Gateway ACL pointed by profile parameter gw/sec_info with help of SAP note 1408081
  • Filter out access from untrusted sources to the Gateway (port tcp/33NN)

Message Server

  • Implement secure Message Server ACL in the file pointed by the profile parameter ms/acl_info, that will help you restrict within the SAP server VLAN only those authorized to connect to. See SAP notes 821875 and 1421005
  • Filter out access from untrusted sources to the Message Server internal port (tcp/39NN) of all your SAP instances

Assessment

You should make sure you know all your assets, especially those that are internet exposed.

Gateway threat

You can check all your landscape with the anonGW code by trying to execute for instance OS command whoami

Message Server threat

Assessing this one is a bit more tricky, as the "be_trusted" PoC is not 100% reliable and may have side effects on Logon Group availability. We strongly do not advise testing on production systems.

If you really want to showcase that during a blackbox assessment, you better choose a landscape that is not user-facing.

For whitebox, you can assume the issue exists if both condition are met:

  • The file pointed by the ms/acl_info profile parameter contains HOST=*
  • The MS internal port tcp/39NN is available from the user VLAN
  • The Gateway port tcp/33NN is available from the user VLAN

Moreover you can use scripts from SecureAuth's Martin Gallo ms_dump_info.py and ms_dump_param.py to remotely check profile parameters against the Message Server internal port, as described in this thread https://twitter.com/MartinGalloAr/status/1124347630555938820

Internet

What about those world maps with scary numbers?

That is SAP specialized TCP SYN scans to detect presence of a specific SAP service (here SAP Gateway, SAP Router, SAP Message Server) behind a certain port. That DOES NOT imply that the services are affected by the discussed vulnerabilities. It is here to help quantify the "external threat" and show that backend servers holding usually sensitive data can be exposed via internet.

That is specialized in a way that usual search scan engines like shodan, censys, zoomeye or onyphe does not yet fully provide this information.

Links

At the moment the only article we think is valuable to be read is this one.

All the other articles related to our research looks like news orders with sole interviewee a company which is selling SAP security tools and consultancy.

Greetz

  • Martin Gallo for all his pysap work and advices
  • Joris van de Vis for feedback on testing
  • Onapsis for spreading FUD and the 10KBLAZE name that does not link back to this research
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