Title:NTLM Hash Leak Via Curl NTLM Authentication Status:test Description:Detects the use of curl with NTLM authentication and empty credentials (-u :), which can be abused to leak the currently logged-in user's NTLMv2 challenge-response to an
attacker-controlled server, enabling offline cracking or relay attacks.
When no credentials are provided, the Microsoft-shipped curl passes a NULL identity to Windows SSPI, which automatically falls back to the current user's logon session credentials
stored in LSASS — without requiring a plaintext password.
This behavior is exclusive to the curl binary shipped by Microsoft (available since Windows 10 / Windows Server 2019), which is built with SSPI support.
References: -https://github.com/curl/curl/blob/master/lib/vauth/ntlm_sspi.c#L128-L140 -https://learn.microsoft.com/en-us/windows/win32/secauthn/acquirecredentialshandle--ntlm -https://curl.se/docs/manpage.html#--ntlm Author: Swachchhanda Shrawan Poudel (Nextron Systems) Date: 2026-06-04 modified:None Tags:
-'attack.credential-access'
-'attack.t1187'
Logsource:
category: process_creation
product: windows
Detection: selection_img: Image|endswith:'\curl.exe'OriginalFileName:'curl.exe'selection_ntlm_flag: CommandLine|contains:
'--ntlm' selection_empty_creds: CommandLine|re:
'(?i)\s(-u|--user)\s*:' condition:all of selection_* Falsepositives:
-Should be very rare as it's not widely known or used, but could occur in legitimate use cases where curl is used with NTLM authentication and empty credentials, such as in certain scripts or automation tasks. Level:high
