Microsoft Outlook Elevation of Privilege Vulnerability (CVE-2023-23397)

Regarding: CVE-2023-23397

This is a fast publish, use at own risk.

See guidance from Microsoft: CVE-2023-23397 – Security Update Guide – Microsoft – Microsoft Outlook Elevation of Privilege Vulnerability

If you need to mitigate the latest Outlook vulnerability which abuses an SMB/WebDav call using the Calendar invite feature you can consider the following:

Education

Some TOX Clients Leak Egress IP addresses

Some friends and I did some testing this evening with TOX clients. We wanted to take a look at PERSEC/OPSEC considerations for using TOX. I also had a sneaky suspicion that it might out of the box leak more than people would appreciate (just a hunch and you don’t know until you test right!).

So, we setup a test. In the test we had:

Threat Intel

DNSSEC – why not having a signed zone is…

Firstly, what is DNSSEC?

https://www.icann.org/resources/pages/dnssec-what-is-it-why-important-2019-03-05-en

Ok read all that good. What we are talking about here is signing a DNS zone to “assure” that the client is getting DNS responses from the right ZONE data. DNSSEC does not encrypt the conversation between DNS client and DNS server. It does enable the client to be able to check if the data it gets back is valid. In short what we are doing is validating that the “data” being returned is authorized and not tampered with.

Threat Intel

ESXiargs Summary 09-02-2023 10:03

What do we know?

Adversary: Unknown, likely Criminal Actor/s

Initial Access Vector: Unknown/Unproven

Impact: ~3K+ Hosts have had Remote Code Execute and their ESXi logon pages changed (plus had encryption routines run to encrypt virtual machines, with varying success). A Second encryption routine has been deployed to some hosts; the threat actor is expanding/changing capabilities.

Risk: Further impact, Additional Threat Actors Exploit the vulnerability

Vulnerabilities

Exploitation of Microsoft Exchange Servers seen in the wild

LATEST UPDATE (04/10/2022)

The latest guidance from Microsoft (released on the 02/10/2022) says to disable administrators from being able to execute remote PowerShell via the exchange PowerShell web endpoint /PowerShell

Customer Guidance for Reported Zero-day Vulnerabilities in Microsoft Exchange Server – Microsoft Security Response Center

October 2, 2022 updates:

Added to the Mitigations section: we strongly recommend Exchange Server customers to disable remote PowerShell access for non-admin users in your organization. Guidance on how to do this for single user or multiple users is here.
Updated Detection section to refer to Analyzing attacks using the Exchange vulnerabilities CVE-2022-41040 and CVE-2022-41082.

Additional mitigations

Remove exchange web services from the internet (there are reasons to do and not do this)
Restrict hybrid servers to allow OWA to O365 only
Leverage dynamic blocking
Greynoise has a list of IPs known here: https://api.greynoise.io/v3/tags/8bf9b766-bf0f-452f-80bf-1d0903847793/ips?format=txt&token=rYZCpLOTf6UnUbBoUpF3Q

Obviously bear in mind this needs auth! but also auth isn’t always that hard..

Microsoft Research have just released (0825 30/09/2022) this: Customer Guidance for Reported Zero-day Vulnerabilities in Microsoft Exchange Server – Microsoft Security Response Center

Microsoft have released a Exchange Server Emergency Mitigation (EMS) which includes URL re-write rules to HELP mitigate this (but likely don’t eliminate all risks due to potential bypasses)

New security feature in September 2021 Cumulative Update for Exchange Server – Microsoft Tech Community

Current Scenario (Updated 11:27 30/09/2022)

Likely “Zero day” exploit in the wild being used to attack exchange servers via a simmilar endpoint to ProxyShell. A mitigation is to apply URL rewrite rules, or to disconect the service internet from untrsuted networks until a patch is available. The Exploit is reported to required AUTHENTICATION, which may significantly limit the volume of exploitation (however credentials are only a phish away). It’s also reported the exploitation in the wild used /Powershell after exploiting the autodiscover endpoint.

Overview (orginal post area)

Yesterday it was reported there was a “new” zero day vulnerability being exploited in the wild. But there appears to be some confusion and a lack of speciifc evidence to showcase the vulnerability being “new” or simply being a differnt exploit path/approach for an existing CVE (e.g. ProxyShell).

The situation from my pov (at time of writing) is still unclear. It would be odd to not advise people ensure they are running the latest supported Exchange CU and Security update release (check both!) – if the exploits are 0-day (which it looks like they are) you will need to also patch when MS release a patch!

You may also wish to: use a WAF/Web Platform (IIS or reverse proxy) to restrict access to potentially vulnreable strings/endpoints.
You should probably review vendor guidance (Microsoft)
You may want to review your exchange servers for indicators of compromise (IOCs)
Check log files for activity, Check for dropped webshells, Check process logs (if you have them!)
Microsoft Recomends using the URL re-write module see (Customer Guidance for Reported Zero-day Vulnerabilities in Microsoft Exchange Server – Microsoft Security Response Center

New Microsoft Exchange zero-days actively exploited in attacks (bleepingcomputer.com)

Upcoming | Zero Day Initiative

Warning: New attack campaign utilized a new 0-day RCE vulnerability on Microsoft Exchange Server | Blog | GTSC – Cung cấp các dịch vụ bảo mật toàn diện (gteltsc.vn)

https://www.shodan.io/search/report?query=http.title%3Aoutlook+exchange

There are 201,995 Exchange Servers with Outlook Web Access Exposed (According to Shodan)

cve-2021-31206 (19,311)
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-31206

9.5% of the worlds Exchange attack surface is vulnerable to CVE-2021-31206

PROXYSHELL

https://www.cisa.gov/uscert/ncas/current-activity/2021/08/21/urgent-protect-against-active-exploitation-proxyshell

CVE-2021-34473 (4388)
CVE-2021-34523 (4388)
CVE-2021-31207 (4388)

2.1% of the worlds Exchange attack surface is vulnerable to ProxyShell CVEs (above) (based on the shodan data)

https://learn.microsoft.com/en-us/exchange/new-features/updates?view=exchserver-2019

Exchange CU Versions

IMPORTANT: Your NEED the LATEST Cummualative Update (CU) and the LATEST Security Updates (SU) for Exchange (and given this is a likely zero day scenario you will need to patch again when the latest patches are released from MS)

https://learn.microsoft.com/en-us/exchange/new-features/updates?view=exchserver-2019

Exchange 2019 CU12 Aug22SU

https://support.microsoft.com/en-gb/topic/description-of-the-security-update-for-microsoft-exchange-server-2019-and-2016-august-9-2022-kb5015322-86c06afb-97df-4d8f-af88-818419db8481

Exchange 2016 CU 23 Aug22SU

https://learn.microsoft.com/en-gb/Exchange/new-features/build-numbers-and-release-dates?view=exchserver-2019

https://support.microsoft.com/en-gb/topic/description-of-the-security-update-for-microsoft-exchange-server-2019-and-2016-august-9-2022-kb5015322-86c06afb-97df-4d8f-af88-818419db8481

Exchange Server 2013 CU23 Aug22SU

https://support.microsoft.com/en-gb/topic/description-of-the-security-update-for-microsoft-exchange-server-2013-august-9-2022-kb5015321-96a47598-09b7-43eb-98bb-76fdf906f265

https://www.microsoft.com/en-us/download/confirmation.aspx?id=58392

Summary

The situation appears to be evolving, as always security vulnerabilities and in the wild exploitations can be a fast moving landscape, internet facing systems need suitable and adequate protections, that doesn’t include just exposing IIS on TCP 443 and walking away. It requires capabilities such as:

WAF/CDN
DoS/DDoS Defence Considerations
Logging and Alerting
Staff to monitor and respond
Secure Configurations
Antirivurs/Antimalware
Segemntation
Endpoint Detection and Response Capabilities (EDR)
Incident Response Planning
Threat Intelligence

and many more things!

This post is a fast publish and may contain errors and/or the situation may change. I’ll try and keep it updated.

Defence

Offensive KEV Alpha 0.1

Working out what exploits to care about is a tough job, kill chains, availability of exploits, complexity, data flows, controls etc. all play a part in understanding a vulnerability and how it affects your organisational risk. To support this effort I’ve started to compile a list of public exploits against CISA Known Exploited Vulnerabilities (KEV). This may be useful for defensive and offensive security pros.

Hacking

Linux Privilege Escalation

When you gain access to a target node you will want to explore, the exact method you use to do this will depend upon operational security considerations, time constraints and style. You will be looking for a range of elements to support progressing an objective.

It should be noted that the objective may NOT require elevation. You may be trying to obtain data and access might already be possible using the context you have assumed.

You also may need to move from a www-data user to a named user account or get to root level of access. If so there’s a range of questions we should be asking ourselves:

Defence

Offensive KEV Updates! CISA releases 38 more CVEs to…

Life in the vulnerability and exploit space is never dull

Spotted on twitter (thanks Danny!):

already ahead of u 😉 you know that all the infosec pros have to read every one…. well ones relvent to their environment/scope…. 😛 x pic.twitter.com/AnMqiLjNvB
— MrR3b00t | #StandWithUkraine #DefendAsOne (@UK_Daniel_Card) June 9, 2022

https://www.zdnet.com/article/cisa-warning-hackers-are-exploiting-these-36-significant-cybersecurity-vulnerabilities-so-patch-now/

CISA updates the known exploited vulnerabilities list (KEV) yesterday with another 38 updates!

That means an update is required for OFFESNIVE KEV!

Education

PWNDEFND: Known Exploitable Vulnerabilities (KEV) – AKA: Offensive KEV

There’s thousand of vulnerabilities, but do you ever struggle work out what ones might actually be useful to you if you are defending or attacking?

Well don’t worry I’ve started to document some things that might help you both attack and defend in CYBERSPACE!

Education

Passive Port Scanners & Internet Asset Discovery Platforms

Useful for a range of defensive and offensive purposes, internet asset search platforms enable a range of activities from:

Research & Trend Analysis
Vulnerability Hunting
Attack Surface Mapping
OSINT

Each has its own interfaces, features, dataset sand styles.

I’ve put together a list of the most popular, there may be more that I haven’t listed.

Firstly, what is DNSSEC?

What do we know?

LATEST UPDATE (04/10/2022)

Additional mitigations

Current Scenario (Updated 11:27 30/09/2022)

Overview (orginal post area)

Global Attack Surface

PROXYSHELL

Exchange CU Versions

IMPORTANT: Your NEED the LATEST Cummualative Update (CU) and the LATEST Security Updates (SU) for Exchange (and given this is a likely zero day scenario you will need to patch again when the latest patches are released from MS)

Exchange 2019 CU12 Aug22SU

Exchange 2016 CU 23 Aug22SU

Exchange Server 2013 CU23 Aug22SU

Summary

Life in the vulnerability and exploit space is never dull