ProxyLogon fixes for unsupported Microsoft Exchange versions released
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2021-26855 | Unauthenticated SSRF/RCE in Microsoft Exchange Server (ProxyLogon) CVE-2021-26855 is a server-side request forgery flaw (CWE-918) in Microsoft Exchange Server that allows an unauthenticated remote attacker to send specially crafted HTTP requests and have the Exchange server process them as itself, disclosing sensitive session information. When chained with sibling Exchange flaws (the 'ProxyLogon' chain), it yields authentication bypass and arbitrary file write, escalating to full remote code execution with SYSTEM-level privileges on the on-premises Exchange server. Any organization running an affected on-premises Exchange server reachable over HTTP/HTTPS (typically outbound webmail) is exposed; Exchange Online was not affected. Exploitation is confirmed in the wild at large scale: the flaw was mass-exploited beginning in early 2021 (notably by the HAFNIUM group), is on the CISA KEV with documented ransomware use, and has a maximum EPSS score of 100% (100th percentile), despite no public PoC listing. Do: Apply the vendor's March 2021 Exchange security updates (or later cumulative updates) immediately, per the CISA required action; until patched, limit Exchange (ECP/OWA) exposure to the internet via firewall/VPN rules. Hunt for compromise: review IIS logs for unrecognized authenticated activity against FrontEnd HttpProxy endpoints, and check for malicious files or webshells under inetpub\wwwroot\aspnet_client, given the known ransomware use. | 9.1 group max | 100% | KEV ransomware PoC ×4 |
| masshundreds of thousands of on-premises deployments; tens of thousands of internet-exposed Exchange servers |
Full article435 words · extracted from securityaffairs.com · click to collapse
Microsoft released ProxyLogon security updates for Microsoft Exchange servers running vulnerable unsupported Cumulative Update versions.
On March 2nd, Microsoft has released emergency out-of-band security updates that address four zero-day issues (CVE-2021-26855, CVE-2021-26857, CVE-2021-26858, and CVE-2021-27065) in all supported Microsoft Exchange versions that are actively exploited in the wild.
Now Microsoft has released security updates for Microsoft Exchange servers running unsupported Cumulative Update versions that are affected by the above vulnerabilities, collectively tracked as ProxyLogon.
The IT giant reported that at least one China-linked APT group, tracked as HAFNIUM, chained these vulnerabilities to access on-premises Exchange servers to access email accounts, and install backdoors to maintain access to victim environments. According to Microsoft, the Hafnium APT exploited these vulnerabilities in targeted attacks against US organizations.
The US Cybersecurity and Infrastructure Security Agency (CISA) has issued the Emergency Directive 21-02 in response to the disclosure of zero-day vulnerabilities in Microsoft Exchange. The US CISA ordered federal agencies to urgently update or disconnect MS Exchange on-premises installs.
Microsoft’s move aims to temporarily protect the servers of its customers until they can install the latest updates for the Exchange servers.
“To help customers more quickly protect their environments in light of the March 2021 Exchange Server Security Updates, Microsoft is producing an additional series of security updates (SUs) that can be applied to some older (and unsupported) Cumulative Updates (CUs).” state the Microsoft Exchange team. “This is intended only as a temporary measure to help you protect vulnerable machines right now. You still need to update to the latest supported CU and then apply the applicable SUs. If you are already mid-update to a later CU, you should continue with that update.”
To install the updates follow this step-by-step procedure:
- Download the update but do not run it immediately.
- Temporarily disable file-level antivirus software
- Select Start, and type CMD.
- In the results, right-click Command Prompt, and then select Run as administrator.
- If the User Account Control dialog box appears, choose Yes, and then select Continue.
- Type the full path of the .msp file, and then press Enter.
- After the installation is finished, re-enable the antivirus software, and then restart the computer. (You might be prompted by the installer to restart.)
Microsoft has also updated its Microsoft Safety Scanner (MSERT) tool to detect web shells employed in the recent Exchange Server attacks.
If you want to receive the weekly Security Affairs Newsletter for free subscribe here.
Follow me on Twitter: @securityaffairs and Facebook
| [adrotate banner=”9″] | [adrotate banner=”12″] |
(SecurityAffairs – hacking, GootKit)
[adrotate banner=”5″]
[adrotate banner=”13″]
Text extracted automatically; images, tables and formatting may be missing. Original: https://securityaffairs.com/115428/security/microsoft-exchange-emergency-update.html