312-49 · Question #318
312-49 Question #318: Real Exam Question with Answer & Explanation
The correct answer is A: An IDS evasion technique. The log shows a FIN scan (IDS27/FIN Scan) from 194.222.156.169. A FIN scan is a classic IDS evasion technique: instead of sending a SYN packet (which firewalls and IDS systems actively monitor), the attacker sends a TCP FIN packet to probe for open ports. RFC-compliant closed por
Question
The following excerpt is taken from a honeypot log. The log captures activities across three days. There are several intrusion attempts; however, a few are successful. (Note: The objective of this question is to test whether the student can read basic information from log entries and interpret the nature of attack.) Apr 24 14:46:46 [4663]: spp_portscan: portscan detected from 194.222.156.169 Apr 24 14:46:46 [4663]: IDS27/FIN Scan: 194.222.156.169:56693 -> 172.16.1.107:482 Apr 24 18:01:05 [4663]: IDS/DNS-version-query: 212.244.97.121:3485 -> 172.16.1.107:53 Apr 24 19:04:01 [4663]: IDS213/ftp-passwd-retrieval: 194.222.156.169:1425 -> 172.16.1.107:21 Apr 25 08:02:41 [5875]: spp_portscan: PORTSCAN DETECTED from 24.9.255.53 Apr 25 02:08:07 [5875]: IDS277/DNS-version-query: 63.226.81.13:4499 -> 172.16.1.107:53 Apr 25 02:08:07 [5875]: IDS277/DNS-version-query: 63.226.81.13:4630 -> 172.16.1.101:53 Apr 25 02:38:17 [5875]: IDS/RPC-rpcinfo-query: 212.251.1.94:642 -> 172.16.1.107:111 Apr 25 19:37:32 [5875]: IDS230/web-cgi-space-wildcard: 198.173.35.164:4221 -> 172.16.1.107:80 Apr 26 05:45:12 [6283]: IDS212/dns-zone-transfer: 38.31.107.87:2291 -> 172.16.1.101:53 Apr 26 06:43:05 [6283]: IDS181/nops-x86: 63.226.81.13:1351 -> 172.16.1.107:53 Apr 26 06:44:25 victim7 PAM_pwdb[12509]: (login) session opened for user simple by (uid=0) Apr 26 06:44:36 victim7 PAM_pwdb[12521]: (su) session opened for user simon by simple(uid=506) Apr 26 06:45:34 [6283]: IDS175/socks-probe: 24.112.167.35:20 -> 172.16.1.107:1080 Apr 26 06:52:10 [6283]: IDS127/telnet-login-incorrect: 172.16.1.107:23 -> 213.28.22.189:4558 From the options given below choose the one which best interprets the following entry: Apr 26 06:43:05 [6283]: IDS181/nops-x86: 63.226.81.13:1351 -> 172.16.1.107:53
Options
- AAn IDS evasion technique
- BA buffer overflow attempt
- CA DNS zone transfer
- DData being retrieved from 63.226.81.13
Explanation
The log shows a FIN scan (IDS27/FIN Scan) from 194.222.156.169. A FIN scan is a classic IDS evasion technique: instead of sending a SYN packet (which firewalls and IDS systems actively monitor), the attacker sends a TCP FIN packet to probe for open ports. RFC-compliant closed ports respond with RST, while open ports typically ignore the packet. Because FIN packets are associated with closing connections rather than initiating them, many older IDS and firewall rules do not flag them, allowing the attacker to enumerate ports while evading detection.
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