OK, I found out at least one mistake I made: when using command line, grabbed from strace output I forgot to remove commas: SO, this line gives /usr/bin/ntlm_auth "--request-nt-key", "--username=freeradius.test", "--domain=LOCAL", "--challenge=0x7c68b9721c3a0b46", "--nt-response=13e96b497efab1bd69bfdcb845393f54e1cd4d71aa7e604a" Logon failure (0xc000006d) And corrected command line gives /usr/bin/ntlm_auth --request-nt-key --username=freeradius.test --domain=LOCAL --challenge=0x7c68b9721c3a0b46 --nt-response=13e96b497efab1bd69bfdcb845393f54e1cd4d71aa7e604a NT_KEY: 9BBCFC30D5E235BBEC00B013372B14E4 Whitch is, I suppose, correct answer. Why it does not work inside freeradius still remains mystery to me. A.