# CVE-2020-1938

### 基本信息#

When using the Apache JServ Protocol (AJP), care must be taken when trusting incoming connections to Apache Tomcat. Tomcat treats AJP connections as having higher trust than, for example, a similar HTTP connection. If such connections are available to an attacker, they can be exploited in ways that may be surprising. In Apache Tomcat 9.0.0.M1 to 9.0.0.30, 8.5.0 to 8.5.50 and 7.0.0 to 7.0.99, Tomcat shipped with an AJP Connector enabled by default that listened on all configured IP addresses. It was expected (and recommended in the security guide) that this Connector would be disabled if not required. This vulnerability report identified a mechanism that allowed: - returning arbitrary files from anywhere in the web application - processing any file in the web application as a JSP Further, if the web application allowed file upload and stored those files within the web application (or the attacker was able to control the content of the web application by some other means) then this, along with the ability to process a file as a JSP, made remote code execution possible. It is important to note that mitigation is only required if an AJP port is accessible to untrusted users. Users wishing to take a defence-in-depth approach and block the vector that permits returning arbitrary files and execution as JSP may upgrade to Apache Tomcat 9.0.31, 8.5.51 or 7.0.100 or later. A number of changes were made to the default AJP Connector configuration in 9.0.31 to harden the default configuration. It is likely that users upgrading to 9.0.31, 8.5.51 or 7.0.100 or later will need to make small changes to their configurations.

• 7.0.0 - 7.0.99
• 8.5.0 - 8.5.50
• 9.0.0.M1 - 9.0.0.30

### 漏洞复现#

#### 环境配置#

./conf/server.xml中默认已默认打开AJP

### 原理#

#### Request Prepare#

./java/org/apache/coyote/ajp/AjpProcessor.java

./java/org/apache/coyote/ajp/AbstractAjpProcessor.java

#### Request Process#

./java/org/apache/coyote/ajp/AjpProcessor.java

Jsp后缀处理

./java/org/apache/jasper/servlet/JspServlet.java :service

./java/org/apache/jasper/servlet/JspServlet.java :serviceJspFile

DefaultSerlvet类继承自HttpServlet，对于Get请求，使用doGet方法读取对应的内容作为response

./java/javax/servlet/http/HttpServlet.java:service

#### 防护方法#

1. 原本默认开启的AJP服务被设置为默认关闭
2. 建议用户在使用AJP服务时使用安全认证机制
3. 对含有任意请求属性的访问返回403（拒绝exp中控制设置的属性的ajp请求）
4. patch链接：