CVE-2022-41040 and CVE-2022-41082: ProxyShell Variant Exploited in the Wild

Microsoft has confirmed reports of two zero-day vulnerabilities in Microsoft Exchange Server that have been exploited in the wild. Patches are not yet available.

Update October 6: The Identifying affected systems section has been updated to reflect a new plugin release.

View Change Log

Background

On September 28, GTSC Cybersecurity Technology Company Limited published a blog post (English translation published later) regarding their discovery of two zero-day vulnerabilities in Microsoft Exchange Server. According to GTSC, its Security Operations Center team discovered the exploitation in August 2022 during its “security monitoring & incident response services.”

GTSC reported these vulnerabilities through Trend Micro’s Zero Day Initiative (ZDI) but, seeing more evidence of exploitation against other targets, decided to publish information about the flaws along with indicators of compromise and mitigation guidance to help organizations defend against attacks.

Late on September 29, Microsoft confirmed the vulnerabilities and assigned CVEs — CVE-2022-41040 and CVE-2022-41082 — but has yet to release patches, stating “we are working on an accelerated timeline to release a fix.” On September 30, Microsoft published an additional blog post with further mitigation instructions and, on October 3, it published advisory pages for both flaws.

Analysis

CVE-2022-41040 is an authenticated server-side request forgery vulnerability in Microsoft Exchange Servers that was assigned a CVSSv3 score of 6.3 by ZDI. Exploitation of CVE-2022-41040 could allow an attacker to exploit CVE-2022-41082.

CVE-2022-41082 is an authenticated remote code execution vulnerability assigned a CVSSv3 score of 8.8. It is very similar to ProxyShell, a chain of three vulnerabilities in Exchange Server discovered by Orange Tsai in 2021. However, the original ProxyShell attack chain did not require authentication, while CVE-2022-41082 does.

Looks like a neat variant!

— Orange Tsai 🍊 (@orange_8361) September 29, 2022

Proof of concept

The team at GTSC provided details of the post-exploitation activity it observed in attacks exploiting these vulnerabilities, but were careful not to publish a detailed proof-of-concept (PoC). No public PoC has been identified yet.

Vendor response

At the time of publication, Microsoft has confirmed these vulnerabilities, but has not released patches. It has provided mitigation and detection guidance. Organizations deploying Microsoft Exchange on-prem should follow the instructions provided by Microsoft to add a new blocking rule to the internet information services manager and disable remote Powershell access wherever possible. We will provide updated patching and mitigation guidance once it is available.

On September 29, Microsoft released a blog post with additional information on detection and mitigation for these vulnerabilities. On October 4, Microsoft updated the mitigation guidance in response to testing by security researchers that proved the original mitigations could be bypassed. 

Identifying affected systems

A list of Tenable plugins to identify these vulnerabilities will appear here as they’re released. This link uses a search filter to ensure that all matching plugin coverage will appear as it is released. When patches are released by Microsoft, additional plugins will be released to identify impacted systems.

While additional plugin coverage is being investigated, we do recommend utilizing the following plugins to identify Microsoft Exchange hosts in your environment:

Plugin ID 108804 – Microsoft Exchange Server Detection (Uncredentialed)
Plugin ID 77910 – Microsoft Exchange Installed

In addition, Tenable has released a new plugin (Plugin ID 165705) which will report all currently supported versions of Microsoft Exchange with a High severity rating. This will aid our customers in identifying systems with Microsoft Exchange installed that are currently affected by the unpatched zero-day vulnerabilities. This plugin is available as of Nessus Plugin Feed Serial ID 202210060050.

Get more information

Microsoft Blog Post: Customer Guidance for Reported Zero-day Vulnerabilities in Microsoft Exchange Server
Microsoft Blog Post: Analyzing attacks using the Exchange vulnerabilities CVE-2022-41040 and CVE-2022-41082
GTSC Cybersecurity Technology Company Limited’s Write Up (English Language)

Join Tenable’s Security Response Team on the Tenable Community.

Learn more about Tenable, the first Cyber Exposure platform for holistic management of your modern attack surface.

Get a free 30-day trial of Tenable.io Vulnerability Management.

Change Log

Update October 6: The Identifying affected systems section has been updated to reflect a new plugin release.

Update October 5: The Vendor Response section has been updated to reflect new mitigation guidance from Microsoft.

Update October 4:The Identifying affected systems section has been updated with additional guidance.

Update October 3: The Background and Vendor Response sections have been updated based on new blog posts and advisories from Microsoft.

 Microsoft has confirmed reports of two zero-day vulnerabilities in Microsoft Exchange Server that have been exploited in the wild. Patches are not yet available.

Update October 6: The Identifying affected systems section has been updated to reflect a new plugin release.

View Change Log

Background

On September 28, GTSC Cybersecurity Technology Company Limited published a blog post (English translation published later) regarding their discovery of two zero-day vulnerabilities in Microsoft Exchange Server. According to GTSC, its Security Operations Center team discovered the exploitation in August 2022 during its “security monitoring & incident response services.”

GTSC reported these vulnerabilities through Trend Micro’s Zero Day Initiative (ZDI) but, seeing more evidence of exploitation against other targets, decided to publish information about the flaws along with indicators of compromise and mitigation guidance to help organizations defend against attacks.

Late on September 29, Microsoft confirmed the vulnerabilities and assigned CVEs — CVE-2022-41040 and CVE-2022-41082 — but has yet to release patches, stating “we are working on an accelerated timeline to release a fix.” On September 30, Microsoft published an additional blog post with further mitigation instructions and, on October 3, it published advisory pages for both flaws.

Analysis

CVE-2022-41040 is an authenticated server-side request forgery vulnerability in Microsoft Exchange Servers that was assigned a CVSSv3 score of 6.3 by ZDI. Exploitation of CVE-2022-41040 could allow an attacker to exploit CVE-2022-41082.

CVE-2022-41082 is an authenticated remote code execution vulnerability assigned a CVSSv3 score of 8.8. It is very similar to ProxyShell, a chain of three vulnerabilities in Exchange Server discovered by Orange Tsai in 2021. However, the original ProxyShell attack chain did not require authentication, while CVE-2022-41082 does.

Looks like a neat variant!
— Orange Tsai 🍊 (@orange_8361) September 29, 2022

Proof of concept

The team at GTSC provided details of the post-exploitation activity it observed in attacks exploiting these vulnerabilities, but were careful not to publish a detailed proof-of-concept (PoC). No public PoC has been identified yet.

Vendor response

At the time of publication, Microsoft has confirmed these vulnerabilities, but has not released patches. It has provided mitigation and detection guidance. Organizations deploying Microsoft Exchange on-prem should follow the instructions provided by Microsoft to add a new blocking rule to the internet information services manager and disable remote Powershell access wherever possible. We will provide updated patching and mitigation guidance once it is available.

On September 29, Microsoft released a blog post with additional information on detection and mitigation for these vulnerabilities. On October 4, Microsoft updated the mitigation guidance in response to testing by security researchers that proved the original mitigations could be bypassed. 

Identifying affected systems

A list of Tenable plugins to identify these vulnerabilities will appear here as they’re released. This link uses a search filter to ensure that all matching plugin coverage will appear as it is released. When patches are released by Microsoft, additional plugins will be released to identify impacted systems.

While additional plugin coverage is being investigated, we do recommend utilizing the following plugins to identify Microsoft Exchange hosts in your environment:

Plugin ID 108804 – Microsoft Exchange Server Detection (Uncredentialed)
Plugin ID 77910 – Microsoft Exchange Installed
In addition, Tenable has released a new plugin (Plugin ID 165705) which will report all currently supported versions of Microsoft Exchange with a High severity rating. This will aid our customers in identifying systems with Microsoft Exchange installed that are currently affected by the unpatched zero-day vulnerabilities. This plugin is available as of Nessus Plugin Feed Serial ID 202210060050.

Get more information

Microsoft Blog Post: Customer Guidance for Reported Zero-day Vulnerabilities in Microsoft Exchange Server
Microsoft Blog Post: Analyzing attacks using the Exchange vulnerabilities CVE-2022-41040 and CVE-2022-41082
GTSC Cybersecurity Technology Company Limited’s Write Up (English Language)

Join Tenable’s Security Response Team on the Tenable Community.

Learn more about Tenable, the first Cyber Exposure platform for holistic management of your modern attack surface.

Get a free 30-day trial of Tenable.io Vulnerability Management.

Change Log

Update October 6: The Identifying affected systems section has been updated to reflect a new plugin release.

Update October 5: The Vendor Response section has been updated to reflect new mitigation guidance from Microsoft.

Update October 4:The Identifying affected systems section has been updated with additional guidance.

Update October 3: The Background and Vendor Response sections have been updated based on new blog posts and advisories from Microsoft. 

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