Experts Reveal New Details on Zero-Click Outlook RCE Exploits

Experts Reveal New Details on Zero-Click Outlook RCE Exploits

Technical details have emerged about two now-patched security flaws in Microsoft Windows that could be chained by threat actors to achieve remote code execution on the Outlook email service sans any user interaction.

The security issues, which were addressed by Microsoft in August and October 2023, respectively, are listed below –

  • CVE-2023-35384 (CVSS score: 5.4) – Windows HTML Platforms Security Feature Bypass Vulnerability
  • CVE-2023-36710 (CVSS score: 7.8) – Windows Media Foundation Core Remote Code Execution Vulnerability

CVE-2023-35384 has been described by Akamai as a bypass for a critical security flaw that Microsoft patched in March 2023. Tracked as CVE-2023-23397 (CVSS score: 9.8), the flaw relates to a case of privilege escalation that could result in the theft of NTLM credentials and enable an attacker to conduct a relay attack.

CVE-2023-35384, like CVE-2023-29324, is rooted in the parsing of a path by the MapUrlToZone function that could be exploited by sending an email containing a malicious file or a URL to an Outlook client.

CVE-2023-36710 impacts the Audio Compression Manager (ACM) component, a legacy Windows multimedia framework that’s used to manage audio codecs, and is the result of an integer overflow vulnerability that occurs when playing a WAV file.

“Finally, we managed to trigger the vulnerability using the IMA ADP codec,” Barnea explained. “The file size is approximately 1.8 GB. By performing the math limit operation on the calculation we can conclude that the smallest possible file size with IMA ADP codec is 1 GB.”

To mitigate the risks, it’s recommended that organizations use microsegmentation to block outgoing SMB connections to remote public IP addresses. Additionally, it also advised to either disable NTLM, or add users to the Protected Users security group, which prevents the use of NTLM as an authentication mechanism.