tcpdump抓取无效TCP标志数据包表达式

最新推荐文章于 2023-07-13 23:49:17 发布

原创最新推荐文章于 2023-07-13 23:49:17 发布 · 4k 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#tcp #gcc

程序应用专栏收录该内容

56 篇文章

订阅专栏

本文通过C语言实现了一个简单的程序来检测TCP包中标志字段的有效性和合法性。通过对TCP标志位的组合进行遍历，筛选出非法的标志组合，并打印出来。

没啥可说的, 直接代码.. :)

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <stdint.h> // TCP 标志 #define TH_FIN 0x01 #define TH_SYN 0x02 #define TH_RST 0x04 #define TH_PUSH 0x08 #define TH_ACK 0x10 #define TH_URG 0x20 #define TH_ECE 0x40 #define TH_CWR 0x80 // TCP 合法标志组合, 标志PUSH, ECE, CWR为一直有效合法标志 static u8 tcp_valid_flags[(TH_FIN|TH_SYN|TH_RST|TH_ACK|TH_URG) + 1] = { [TH_SYN] = 1, [TH_SYN|TH_URG] = 1, [TH_SYN|TH_ACK] = 1, [TH_RST] = 1, [TH_RST|TH_ACK] = 1, [TH_FIN|TH_ACK] = 1, [TH_FIN|TH_ACK|TH_URG] = 1, [TH_ACK] = 1, [TH_ACK|TH_URG] = 1, }; int main(int argc, char **argv) { uint8_t flags_max = 0xff; uint8_t i; uint8_t flags = 0; uint8_t mask = (uint8_t)~(TH_ECE | TH_CWR | TH_PUSH); for( i = 0; i < flags_max; i++ ){ flags = i & mask; if ( tcp_valid_flags[flags] == 0 ) { // 标记已非法标志 tcp_valid_flags[flags] = 0x2; printf("'tcp[13] & 0x%x = 0x%x' or ", mask, flags ); } } printf("/n"); return 0; }

# gcc tcp_flags.c -o tcp_flags

# ./tcp_flags

输出

'tcp[13] & 0x37 = 0x0' or 'tcp[13] & 0x37 = 0x1' or 'tcp[13] & 0x37 = 0x3' or 'tcp[13] & 0x37 = 0x5' or 'tcp[13] & 0x37 = 0x6' or 'tcp[13] & 0x37 = 0x7' or 'tcp[13] & 0x37 = 0x13' or 'tcp[13] & 0x37 = 0x15' or 'tcp[13] & 0x37 = 0x16' or 'tcp[13] & 0x37 = 0x17' or 'tcp[13] & 0x37 = 0x15' or 'tcp[13] & 0x37 = 0x16' or 'tcp[13] & 0x37 = 0x17' or 'tcp[13] & 0x37 = 0x20' or 'tcp[13] & 0x37 = 0x21' or 'tcp[13] & 0x37 = 0x23' or 'tcp[13] & 0x37 = 0x24' or 'tcp[13] & 0x37 = 0x25' or 'tcp[13] & 0x37 = 0x26' or 'tcp[13] & 0x37 = 0x27' or 'tcp[13] & 0x37 = 0x20' or 'tcp[13] & 0x37 = 0x21' or 'tcp[13] & 0x37 = 0x23' or 'tcp[13] & 0x37 = 0x24' or 'tcp[13] & 0x37 = 0x25' or 'tcp[13] & 0x37 = 0x26' or 'tcp[13] & 0x37 = 0x27' or 'tcp[13] & 0x37 = 0x32' or 'tcp[13] & 0x37 = 0x33' or 'tcp[13] & 0x37 = 0x34' or 'tcp[13] & 0x37 = 0x35' or 'tcp[13] & 0x37 = 0x36' or 'tcp[13] & 0x37 = 0x37' or

去掉最后一个or 即是非法TCP标志组合 :)