YARA规则编写与实战指南<\/h1>

1. YARA简介<\/h2>
YARA是一种强大的恶意软件模式匹配工具，可以根据二进制或文本内容进行模式匹配。它广泛应用于恶意软件分析、威胁检测和数字取证领域。<\/p>

2. 基本规则结构<\/h2>

每条YARA规则必须包含一个名称和条件(condition)。最简单的规则如下：<\/p>

rule dummy {
    condition: true
}
<\/code><\/pre>

condition<\/code>是关键字，必须包含一个布尔表达式<\/li>
这个例子中，规则总是会被匹配<\/li>
<\/ul>
3. 运行YARA规则<\/h2>
基本命令格式：<\/p>
yara rule.yar dir
<\/code><\/pre>
常用参数：<\/p>

-r<\/code>：递归搜索<\/li>
-s<\/code>：输出匹配到的字符串<\/li>
-X<\/code>：输出xor key<\/li>
-p<\/code>：多线程处理<\/li>
-c<\/code>：只输出匹配数量<\/li>
<\/ul>
4. 元数据(Meta)<\/h2>
元数据用于标注作者、版本号、描述、哈希等附加信息，不会影响匹配逻辑：<\/p>
rule dummy {
    meta:
        a = 123456
        b = "description"
    condition:
        true
}
<\/code><\/pre>
5. 字符串匹配<\/h2>
YARA支持多种字符串匹配方式：<\/p>
5.1 文本字符串<\/h3>
大小写敏感的普通字符串，可通过修饰符调整匹配行为：<\/p>
rule Example {
    strings:
        $text_string = "Hello World" nocase
    condition:
        $text_string
}
<\/code><\/pre>
常用修饰符：<\/p>

nocase<\/code>：大小写不敏感<\/li>
wide<\/code>：匹配宽字符<\/li>
xor<\/code>：匹配进行1字节异或的字符串变体<\/li>
base64<\/code>：匹配base64编码的字符串变体<\/li>
<\/ul>
5.2 十六进制字符串<\/h3>
支持两种表示形式，支持通配符和非操作(~)：<\/p>
rule HexExample {
    strings:
        $hex_string = { 12 34 56 ?? 78 [2-4] 90 }
    condition:
        $hex_string
}
<\/code><\/pre>
5.3 正则表达式<\/h3>
写在\/<\/code>之间：<\/p>
rule RegExExample {
    strings:
        $re = \/[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\/
    condition:
        $re
}
<\/code><\/pre>
6. 条件表达式<\/h2>
条件部分支持多种逻辑运算和关键字：<\/p>
6.1 基本逻辑运算<\/h3>
condition:
    ($a and $b) or (not $c)
<\/code><\/pre>
6.2 字符串集操作<\/h3>
condition:
    all of them    \/\/ 匹配所有字符串
    1 of them      \/\/ 匹配任意一个字符串
    none of them   \/\/ 不匹配任何字符串
<\/code><\/pre>
6.3 特殊关键字<\/h3>

filesize<\/code>：文件大小<\/li>
entrypoint<\/code>：入口点(高版本已弃用，改用PE模块的entry_point<\/code>)<\/li>
<\/ul>
6.4 循环结构<\/h3>
condition:
    for any of ($a, $b) : ( $ at pe.entry_point )
<\/code><\/pre>
7. 取值操作<\/h2>
可以从指定偏移读取值：<\/p>
condition:
    uint32(0) == 0x5A4D and  \/\/ MZ头
    uint32(uint32(0x3C)) == 0x00004550  \/\/ PE头
<\/code><\/pre>
支持的类型：<\/p>

int8<\/code>, uint8<\/code><\/li>
int16<\/code>, uint16<\/code><\/li>
int32<\/code>, uint32<\/code><\/li>
int64<\/code>, uint64<\/code><\/li>
be<\/code>后缀表示大端序(默认小端序)<\/li>
<\/ul>
8. 实战示例<\/h2>
8.1 检测RWX内存申请<\/h3>
rule RWX_Memory {
    meta:
        description = "Detects RWX memory allocation"
    strings:
        $alloc = { 48 8D 0D ?? ?? ?? ?? 41 B8 40 00 00 00 }  \/\/ PAGE_EXECUTE_READWRITE = 0x40
    condition:
        $alloc
}
<\/code><\/pre>
8.2 检测RC4加密<\/h3>
rule RC4_Encryption {
    meta:
        description = "Detects use of SystemFunction032\/033 for RC4"
    strings:
        $func032 = "SystemFunction032"
        $func033 = "SystemFunction033"
    condition:
        any of them
}
<\/code><\/pre>
8.3 检测高熵无签名代码<\/h3>
rule High_Entropy_No_Signature {
    meta:
        description = "Detects high entropy sections with no signature"
    condition:
        pe.sections[i].entropy > 7.0 and
        not pe.exports("CryptVerifyCertificateSignature")
}
<\/code><\/pre>
9. yara-python使用<\/h2>
官方提供的Python库，用于程序化调用YARA：<\/p>
import<\/span> yara
<\/span><\/span>
<\/span><\/span>rules =<\/span> yara.<\/span>compile(filepath=<\/span>'rules.yar'<\/span>)
<\/span><\/span>
<\/span><\/span>def<\/span> callback<\/span>(data):
<\/span><\/span>    print("Match found:"<\/span>, data)
<\/span><\/span>    return<\/span> yara.<\/span>CALLBACK_CONTINUE
<\/span><\/span>
<\/span><\/span>matches =<\/span> rules.<\/span>match('\/path\/to\/file'<\/span>, callback=<\/span>callback)
<\/span><\/span><\/code><\/pre>回调返回值：<\/p>

CALLBACK_CONTINUE<\/code>：继续搜索<\/li>
CALLBACK_ABORT<\/code>：终止搜索<\/li>
<\/ul>
9.1 进程扫描示例<\/h3>
import<\/span> yara
<\/span><\/span>import<\/span> psutil
<\/span><\/span>
<\/span><\/span>rules =<\/span> yara.<\/span>compile(source=<\/span>'''
<\/span><\/span><\/span>rule RWX_Memory {
<\/span><\/span><\/span>    strings:
<\/span><\/span><\/span>        $alloc = { 48 8D 0D ?? ?? ?? ?? 41 B8 40 00 00 00 }
<\/span><\/span><\/span>    condition:
<\/span><\/span><\/span>        $alloc
<\/span><\/span><\/span>}
<\/span><\/span><\/span>'''<\/span>)
<\/span><\/span>
<\/span><\/span>for<\/span> proc in<\/span> psutil.<\/span>process_iter():
<\/span><\/span>    try<\/span>:
<\/span><\/span>        matches =<\/span> rules.<\/span>match(pid=<\/span>proc.<\/span>pid)
<\/span><\/span>        if<\/span> matches:
<\/span><\/span>            print(f<\/span>"Found in PID <\/span>{<\/span>proc.<\/span>pid}<\/span>, killing..."<\/span>)
<\/span><\/span>            proc.<\/span>kill()
<\/span><\/span>    except<\/span>:
<\/span><\/span>        continue<\/span>
<\/span><\/span><\/code><\/pre>10. yarGen工具使用<\/h2>
yarGen是一款自动生成YARA规则的工具：<\/p>
基本用法：<\/p>
python yarGen.py -m suspicious_dir --excludegood -o rules.yar
<\/code><\/pre>
参数说明：<\/p>

-m<\/code>：指定恶意样本目录<\/li>
--excludegood<\/code>：排除良性字符串<\/li>
-o<\/code>：输出规则文件<\/li>
<\/ul>
11. 规避技巧<\/h2>
从生成的规则中可以看出一些规避YARA检测的方法：<\/p>

完全规避CRT(C运行时库)的使用<\/li>
删除PDB调试信息<\/li>
使用非常规字符串编码<\/li>
避免使用明显的API调用模式<\/li>
<\/ol>
12. 最佳实践<\/h2>

规则应尽可能具体，减少误报<\/li>
使用元数据提供足够的信息<\/li>
结合多种检测条件提高准确性<\/li>
定期更新规则以适应新的威胁<\/li>
测试规则确保不会产生过多误报<\/li>
<\/ol>
通过掌握这些YARA规则编写技巧，您可以有效地创建强大的恶意软件检测规则，提高安全分析效率。<\/p>

YARA规则编写与实战指南<\/h1>

1. YARA简介<\/h2> YARA是一种强大的恶意软件模式匹配工具，可以根据二进制或文本内容进行模式匹配。它广泛应用于恶意软件分析、威胁检测和数字取证领域。<\/p>

5. 字符串匹配<\/h2> YARA支持多种字符串匹配方式：<\/p>

6. 条件表达式<\/h2> 条件部分支持多种逻辑运算和关键字：<\/p>

8. 实战示例<\/h2>

1. YARA简介<\/h2>
YARA是一种强大的恶意软件模式匹配工具，可以根据二进制或文本内容进行模式匹配。它广泛应用于恶意软件分析、威胁检测和数字取证领域。<\/p>

5. 字符串匹配<\/h2>
YARA支持多种字符串匹配方式：<\/p>

6. 条件表达式<\/h2>
条件部分支持多种逻辑运算和关键字：<\/p>