当前位置：首页 > news >正文

[实践总结] 限制正则表达式匹配次数/时间防止DoS攻击

news 2025/8/19 13:32:45

思路

1、优化正则表达式
2、正则表达式无法优化的话，可以考虑限制匹配次数，或者限制匹配时间

限制匹配次数

public class CountedCharSequence implements CharSequence {private final CharSequence charSequence;private long count;public CountedCharSequence(CharSequence charSequence, long count) {this.charSequence = charSequence;this.count = count;}@Overridepublic String toString() {return charSequence.toString();}@Overridepublic int length() {return charSequence.length();}@Overridepublic char charAt(int index) {if (index <= 0) {throw new IllegalArgumentException("Regex match over max " + count + " times");}count--;return charSequence.charAt(index);}@Overridepublic CharSequence subSequence(int start, int end) {return charSequence.subSequence(start, end);}
}

模拟Dos攻击

String str = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";long start = System.nanoTime();
Pattern.compile("^(a+)+$").matcher(str).matches();
System.out.println(((System.nanoTime() - start)) + " nano seconds");执行用时
1399200 nano seconds

超过 1亿就会报错

long start1 = System.nanoTime();try {Pattern.compile("^(a+)+$").matcher(new CountedCharSequence(str, 100_000_000)).matches();
} catch (Exception e) {System.out.println(e.getMessage());
}System.out.println(((System.nanoTime() - start1)) + " nano seconds");执行用时
Regex match over max 100000000 times
601800 nano seconds

限制匹配时间

import java.util.regex.Pattern;public final class TimedCharSequence implements CharSequence {private final CharSequence sequence;private final long timestamp;public TimedCharSequence(CharSequence sequence, long nanoseconds) {this.sequence = sequence;this.timestamp = System.nanoTime() + nanoseconds;}@Overridepublic String toString() {return sequence.toString();}@Overridepublic int length() {return sequence.length();}@Overridepublic char charAt(int index) {if (timestamp < System.nanoTime()) {throw new IllegalStateException("Regex match timeout");}return sequence.charAt(index);}@Overridepublic CharSequence subSequence(int start, int end) {return sequence.subSequence(start, end);}
}

模拟Dos攻击

String str = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";long start = System.nanoTime();
Pattern.compile("^(a+)+$").matcher(str).matches();
System.out.println(((System.nanoTime() - start)) + " nano seconds");执行用时：
1385400 nano seconds

超过给定时间间隔就报错

long start1 = System.nanoTime();try {Pattern.compile("^(a+)+$").matcher(new TimedCharSequence(str, 10_000)).matches();
} catch (Exception e) {System.out.println(e.getMessage());
}System.out.println(((System.nanoTime() - start1)) + " nano seconds");执行用时：
Regex match timeout
123100 nano seconds