Analytics Story: Windows Error Reporting Service Elevation of Privilege Vulnerability

Date: 2023-08-24 ID: 64dea1e5-2c60-461f-b886-05580ed89b5c Author: Michael Haag, Splunk Product: Splunk Enterprise Security

Description

In July 2023, CrowdStrike's Falcon Complete managed detection and response (MDR) team uncovered an exploit kit using an unknown vulnerability in the Windows Error Reporting (WER) component. The vulnerability, now identified as CVE-2023-36874, was also independently discovered by Google's Threat Analysis Group. The exploit came to light when suspicious binaries were observed on a European technology system. CrowdStrike's Counter Adversary Operations' analysis revealed a zero-day exploit targeting the WER service, allowing attackers to execute unauthorized code with elevated privileges. The exploit kit seen aimed to spawn a privileged interpreter, displaying the versatility and adaptability of the threat. CrowdStrike has listed some potential indicators of compromise, but these are of low fidelity due to their mutable nature.

Why it matters

In June 2023, CrowdStrike's Falcon Complete team observed suspicious activities on a European technology entity's system. Multiple binaries were dropped onto the system via Remote Desktop Protocol (RDP), some of which were flagged as potential exploits for a known vulnerability. However, a string containing the Russian term for "0day" suggested an unknown vulnerability was at play. Subsequent investigations identified this as a zero-day vulnerability affecting the Windows Error Reporting (WER) component, now known as CVE-2023-36874. The WER service's function is to report software issues on Windows hosts. The exploit centered around manipulating the WER service by redirecting file systems to execute attacker-controlled code with elevated privileges. This was achieved by creating a symbolic link redirection from the C:\ drive to an attacker-controlled directory, and then triggering certain WER functions. Consequently, an unauthorized executable was run instead of the legitimate one, giving the attacker high-level access. The observed exploit kit's primary objective was to initiate a privileged interpreter, such as cmd.exe or powershell_ise.exe. If this couldn't be achieved, a privileged scheduled task was created as an alternative. The exploit kit showcased a range of binaries, some packed and others not, some in C++ and others in pure C. This diversity suggests the knowledge of the vulnerability was likely shared among different developers. CrowdStrike's Counter Adversary Operations, as of now, hasn't linked this activity to any specific threat actor. They've provided potential indicators of compromise, but caution that these are easily changed, indicating the advanced capabilities of the adversaries.

Detections

Name ▲▼ Technique ▲▼ Type ▲▼
System Processes Run From Unexpected Locations Masquerading, Rename System Utilities Anomaly
Windows Process Injection Wermgr Child Process Process Injection Anomaly
WinEvent Scheduled Task Created to Spawn Shell Scheduled Task, Scheduled Task/Job TTP

Data Sources

Name ▲▼ Platform ▲▼ Sourcetype ▲▼ Source ▲▼
CrowdStrike ProcessRollup2 N/A crowdstrike:events:sensor crowdstrike
Sysmon EventID 1 Windows icon Windows xmlwineventlog XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
Windows Event Log Security 4688 Windows icon Windows xmlwineventlog XmlWinEventLog:Security
Windows Event Log Security 4698 Windows icon Windows xmlwineventlog XmlWinEventLog:Security

References

Source: GitHub | Version: 1