Suricata & Iptables cheatsheet

Reading time: 8 minutes

Iptables

Chains

在iptables中，称为链的规则列表是按顺序处理的。在这些链中，三条主要链是普遍存在的，额外的链如NAT可能会根据系统的能力得到支持。

• Input Chain: 用于管理传入连接的行为。
• Forward Chain: 用于处理不指向本地系统的传入连接。这对于充当路由器的设备是典型的，其中接收到的数据旨在转发到另一个目的地。当系统参与路由、NAT或类似活动时，这条链是相关的。
• Output Chain: 专用于调节传出连接。

这些链确保网络流量的有序处理，允许指定详细规则来管理数据流入、流经和流出系统的方式。

# Delete all rules
iptables -F

# List all rules
iptables -L
iptables -S

# Block IP addresses & ports
iptables -I INPUT -s ip1,ip2,ip3 -j DROP
iptables -I INPUT -p tcp --dport 443 -j DROP
iptables -I INPUT -s ip1,ip2 -p tcp --dport 443 -j DROP

# String based drop
## Strings are case sensitive (pretty easy to bypass if you want to check an SQLi for example)
iptables -I INPUT -p tcp --dport <port_listening> -m string --algo bm --string '<payload>' -j DROP
iptables -I OUTPUT -p tcp --sport <port_listening> -m string --algo bm --string 'CTF{' -j DROP
## You can also check for the hex, base64 and double base64 of the expected CTF flag chars

# Drop every input port except some
iptables -P INPUT DROP # Default to drop
iptables -I INPUT -p tcp --dport 8000 -j ACCEPT
iptables -I INPUT -p tcp --dport 443 -j ACCEPT


# Persist Iptables
## Debian/Ubuntu:
apt-get install iptables-persistent
iptables-save > /etc/iptables/rules.v4
ip6tables-save > /etc/iptables/rules.v6
iptables-restore < /etc/iptables/rules.v4
##RHEL/CentOS:
iptables-save > /etc/sysconfig/iptables
ip6tables-save > /etc/sysconfig/ip6tables
iptables-restore < /etc/sysconfig/iptables

Suricata

安装与配置

# Install details from: https://suricata.readthedocs.io/en/suricata-6.0.0/install.html#install-binary-packages
# Ubuntu
add-apt-repository ppa:oisf/suricata-stable
apt-get update
apt-get install suricata

# Debian
echo "deb http://http.debian.net/debian buster-backports main" > \
/etc/apt/sources.list.d/backports.list
apt-get update
apt-get install suricata -t buster-backports

# CentOS
yum install epel-release
yum install suricata

# Get rules
suricata-update
suricata-update list-sources #List sources of the rules
suricata-update enable-source et/open #Add et/open rulesets
suricata-update
## To use the dowloaded rules update the following line in /etc/suricata/suricata.yaml
default-rule-path: /var/lib/suricata/rules
rule-files:
- suricata.rules

# Run
## Add rules in /etc/suricata/rules/suricata.rules
systemctl suricata start
suricata -c /etc/suricata/suricata.yaml -i eth0


# Reload rules
suricatasc -c ruleset-reload-nonblocking
## or set the follogin in /etc/suricata/suricata.yaml
detect-engine:
- rule-reload: true

# Validate suricata config
suricata -T -c /etc/suricata/suricata.yaml -v

# Configure suricata as IPs
## Config drop to generate alerts
## Search for the following lines in /etc/suricata/suricata.yaml and remove comments:
- drop:
alerts: yes
flows: all

## Forward all packages to the queue where suricata can act as IPS
iptables -I INPUT -j NFQUEUE
iptables -I OUTPUT -j NFQUEUE

## Start suricata in IPS mode
suricata -c /etc/suricata/suricata.yaml  -q 0
### or modify the service config file as:
systemctl edit suricata.service

[Service]
ExecStart=
ExecStart=/usr/bin/suricata -c /etc/suricata/suricata.yaml --pidfile /run/suricata.pid -q 0 -vvv
Type=simple

systemctl daemon-reload

规则定义

来自文档： 一条规则/签名由以下部分组成：

• 动作，决定当签名匹配时发生什么。
• 头部，定义规则的协议、IP地址、端口和方向。
• 规则选项，定义规则的具体细节。

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"HTTP GET Request Containing Rule in URI"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"rule"; fast_pattern; classtype:bad-unknown; sid:123; rev:1;)

有效的操作是

• alert - 生成警报
• pass - 停止对数据包的进一步检查
• drop - 丢弃数据包并生成警报
• reject - 向匹配数据包的发送者发送 RST/ICMP 不可达错误。
• rejectsrc - 与 reject 相同
• rejectdst - 向匹配数据包的接收者发送 RST/ICMP 错误数据包。
• rejectboth - 向对话的双方发送 RST/ICMP 错误数据包。

协议

• tcp (用于 tcp 流量)
• udp
• icmp
• ip (ip 代表“所有”或“任何”)
• layer7 协议: http, ftp, tls, smb, dns, ssh... (更多内容见 docs)

源地址和目标地址

它支持 IP 范围、否定和地址列表：

源端口和目标端口

它支持端口范围、否定和端口列表

方向

可以指示所应用的通信规则的方向：

source -> destination
source <> destination  (both directions)

关键词

在 Suricata 中有 数百种选项 可用于搜索您所寻找的 特定数据包，如果发现有趣的内容，这里会提到。请查看 文档以获取更多信息！

# Meta Keywords
msg: "description"; #Set a description to the rule
sid:123 #Set a unique ID to the rule
rev:1 #Rule revision number
config classification: not-suspicious,Not Suspicious Traffic,3 #Classify
reference: url, www.info.com #Reference
priority:1; #Set a priority
metadata: key value, key value; #Extra metadata

# Filter by geolocation
geoip: src,RU;

# ICMP type & Code
itype:<10;
icode:0

# Filter by string
content: "something"
content: |61 61 61| #Hex: AAA
content: "http|3A|//" #Mix string and hex
content: "abc"; nocase; #Case insensitive
reject tcp any any -> any any (msg: "php-rce"; content: "eval"; nocase; metadata: tag php-rce; sid:101; rev: 1;)

# Replaces string
## Content and replace string must have the same length
content:"abc"; replace: "def"
alert tcp any any -> any any (msg: "flag replace"; content: "CTF{a6st"; replace: "CTF{u798"; nocase; sid:100; rev: 1;)
## The replace works in both input and output packets
## But it only modifies the first match

# Filter by regex
pcre:"/<regex>/opts"
pcre:"/NICK .*USA.*[0-9]{3,}/i"
drop tcp any any -> any any (msg:"regex"; pcre:"/CTF\{[\w]{3}/i"; sid:10001;)

# Other examples
## Drop by port
drop tcp any any -> any 8000 (msg:"8000 port"; sid:1000;)