Suspicious CredUI.DLL Loading by Uncommon Processes

This threat brief details a detection for the suspicious loading of credui.dll or wincredui.dll by processes not commonly associated with these system libraries. CredUI.DLL is a legitimate Windows component responsible for displaying credential dialogs and managing credential input. Attackers frequently abuse legitimate system binaries and libraries to perform malicious actions while evading detection. By forcing an uncommon process to load credui.dll, an adversary can potentially leverage functions like CredUIPromptForCredentials or CredUnPackAuthenticationBufferW to capture user credentials or manipulate credential buffers directly. This technique serves as an indicator of post-exploitation activity, signaling attempts to gain access to stored credentials or prompt users for sensitive information. The detection focuses on filtering known legitimate process paths to highlight truly anomalous behavior.

Impact

Successful exploitation of this technique can lead to significant impact, primarily through credential access and theft. Attackers gaining control of user credentials can then perform lateral movement within the network, escalate privileges, access sensitive data, or establish persistence. This can enable further stages of an attack, such as data exfiltration, deployment of ransomware, or critical system disruption. The immediate consequence is the compromise of user accounts, potentially leading to widespread organizational impact if high-privilege credentials are obtained.

Recommendation

• Deploy the Sigma rule "CredUI.DLL Loaded By Uncommon Process" to your SIEM and tune for your environment.
• Ensure image_load logging is enabled for your Windows endpoints, preferably via Sysmon, to collect the necessary telemetry for the provided Sigma rule.
• Investigate all alerts generated by the "CredUI.DLL Loaded By Uncommon Process" rule, focusing on the parent process and its command line arguments.