Proof-of-Concept Code Gives Standard Microsoft Exchange Users Domain Administrator Privileges (CVE-2019-0724, CVE-2019-0686)
Publicly released and newly named “PrivExchange” proof-of-concept (POC) privilege escalation code exploits protocol flaws and default configurations to give standard Exchange users Domain Administrator access.
Contexte
Update February 12: Microsoft released updates for CVE-2019-0724 and CVE-2019-0686 to address this vulnerability.
Update February 6: Microsoft published a security advisory (ADV190007) that includes a Throttling Policy that will mitigate this vulnerability until a software update. Additionally, they noted that the vulnerability described in the blog post below only affects on-prem deployments of Microsoft Exchange. Microsoft notes in the advisory that this workaround might disrupt some functions in Outlook for Mac, Skype for Business Client, Apple Mail Clients and third-party applications.
Previously documented protocol weaknesses and vulnerabilities in fully patched Microsoft Exchange are now in the spotlight due to publicly released POC code. According to security researcher Dirk-Jan Mollema, this vulnerability: “Probably affects the majority of orgs using AD and Exchange.”
The POC code submitted to Github allows a standard Exchange user to gain Domain Administrator access to a fully patched Microsoft Exchange 2016 server and dump domain credentials from the Domain Controller.
Vulnerability Details
This issue is not a single vulnerability, but rather a collection of previously disclosed protocol weaknesses affecting NT LAN Manager (NTLM) authentication and Exchange Server vulnerabilities. Per the researcher’s blog:
- Exchange Servers have (too) high privileges by default
- NTLM authentication is vulnerable to relay attacks
- Exchange has a feature which makes it authenticate to an attacker with the computer account of the Exchange server
Mollema also included a script that reportedly allows for unauthenticated attacks where one could relay the authentication of a user in the same network segment to Exchange Web Services (EWS) and use their credentials to perform the exploit.
Urgently required actions
This issue reportedly affects fully patched Microsoft Exchange servers, however the following mitigations, including one recommended by Microsoft, are listed by the security researcher:
- Remove the unnecessary high privileges that Exchange has on the Domain object (references included below).
- Enable Lightweight Directory Access Protocol (LDAP) signing and enable LDAP channel binding to prevent relaying to LDAP and LDAPS respectively
- Block Exchange servers from making connections to workstations on arbitrary ports.
- Enable Extended Protection for Authentication on the Exchange endpoints in IIS (but not the Exchange Back End ones, this will break Exchange). This will verify the channel binding parameters in the NTLM authentication, which ties NTLM authentication to a TLS connection and prevent relaying to Exchange web services.
- Remove the registry key which makes relaying back to the Exchange server possible, as discussed in Microsoft’s mitigation for CVE-2018-8581. (Tenable provides coverage for this mitigation)
- Enforce SMB signing on Exchange servers (and preferable all other servers and workstations in the domain) to prevent cross-protocol relay attacks to SMB.
Identification des systèmes affectés
A list of Nessus plugins to identify this vulnerability can be found here.
Tenable also provides the mitigation-specific configuration audit checks below for Server Message Block (SMB) signing and NTLM v2 at https://www.tenable.com/downloads/audit using these audit files:
CIS_DC_SERVER_2012_Level_1_v2.0.1.audit
CIS_DC_SERVER_2012_R2_Level_1_v2.3.0.audit
CIS_DC_SERVER_2016_Level_1_v1.0.0.audit
CIS_MS_2008_Server_Enterprise_v1.2.0.audit
CIS_MS_2008_Server_SSLF_v1.2.0.audit
CIS_MS_SERVER_2012_Level_1_v2.0.1.audit
CIS_MS_SERVER_2012_R2_Level_1_v2.3.0.audit
CIS_MS_SERVER_2016_Level_1_v1.0.0.audit
CIS_MS_Windows_10_Enterprise_Level_1_Bitlocker_v1.3.0.audit
CIS_MS_Windows_10_Enterprise_Level_1_v1.3.0.audit
CIS_MS_Windows_Server_2008_DC_Level_1_v3.0.1.audit
CIS_MS_Windows_Server_2008_MS_Level_1_v3.0.1.audit
CIS_MS_Windows_Server_2008_R2_DC_Level_1_v3.1.0.audit
CIS_MS_Windows_Server_2008_R2_MS_Level_1_v3.1.0.audit
DISA_STIG_Server_2008_DC_v6r40.audit
DISA_STIG_Server_2008_MS_v6r40.audit
DISA_STIG_Server_2012_and_2012_R2_DC_v2r12.audit
DISA_STIG_Server_2012_and_2012_R2_MS_v2r12.audit
DISA_STIG_Windows_10_v1r13.audit
DISA_STIG_Windows_Server_2016_v1r4.audit
Où trouver plus d'informations
Learn more about Tenable.io, the first Cyber Exposure platform for holistic management of your modern attack surface. Get a free 60-day trial of Tenable.io Vulnerability Management.
Articles connexes
CVE-2024-20353, CVE-2024-20359: Frequently Asked Questions About ArcaneDoor
April 25, 2024Frequently asked questions about CVE-2024-20353 and CVE-2024-20359, two vulnerabilities associated with “ArcaneDoor,” the espionage-related campaign targeting Cisco Adaptive Security Appliances.
Operational Technology in the DoD: Ensuring a Secure and Efficient Power Grid
April 19, 2024In an evolving threat landscape, the DoD must make sure that its mission-critical operations don’t experience power outages.
Strengthening the Nessus Software Supply Chain with SLSA
April 16, 2024You know Tenable as a cybersecurity industry leader whose world-class exposure management products are trusted by our approximately 43,000 customers, including about 60% of the Fortune 500. But sometimes we like to give you a peek behind the curtain to share how we protect our own house against cyberattacks – and that’s what this blog is about. Today we’re sharing our experience adopting the supply-chain security framework SLSA, with the hopes that the lessons we learned will be helpful to you.
As Pro-Russia Hactivists Target OT Systems, Here’s What You Need To Know
May 2, 2024U.S. and international cybersecurity and law enforcement agencies this week issued a joint fact sheet to highlight and safeguard against the continued malicious cyber activity conducted by pro-Russia hacktivists against operational technology (OT) devices in North America and Europe. Read on to get all the details and learn what actions to take today.
Tenable Bolsters Its Cloud Security Arsenal with Malware Detection
May 1, 2024Tenable Cloud Security is enhancing its capabilities with malware detection. Combined with its cutting-edge, agentless vulnerability-scanning technology, including its ability to detect anomalous behavior, this new capability makes Tenable Cloud Security a much more complete and effective solution. Read on to find out how.
Cybersecurity Snapshot: Latest MITRE ATT&CK Update Offers Security Insights on GenAI, Identity, Cloud and CI/CD
April 26, 2024Check out what’s new in Version 15 of the MITRE ATT&CK knowledge base of adversary tactics, techniques and procedures. Plus, learn the latest details about the Change Healthcare breach, including the massive scope of the data exfiltration. In addition, why AI cyberthreats aren’t impacting CISOs’ budgets. And much more!
- Vulnerability Management