背景
最近用suricata替换了zeek，但是在使用suricata时发现协议解析没有zeek做的细致。正好遇到需要检测mysql弱口令的需求。对比suricata，zeek修改起来难度更低。这篇文章可以帮助同样有检测需求的人，利用zeek实现mysql弱口令的检测。
首先搭建环境抓取MySQL登录认证包如下：
比较关键的报文即三次握手之后，服务器主动发送的Server Greeting和客户端返回的响应Login Request。
在Server Greeting包中，我们可以看到服务器使用的认证插件为mysql_native_password，这也是现在大部分mysql服务器默认的认证方式。
在Login Request包中，我们可以看到客户端向服务器发送的username和password，这里明文密码是123456，可以看到在mysql_native_password插件认证方式下，明文密码被替换成了hash值进行传输。
多登录几次并进行抓包，可以发现password的hash值是不断变化的。根据go语言版本的mysql驱动源码，我们可以了解到客户端在做登录认证时，如何处理的明文密码：
// Hash password using 4.1+ method (SHA1)func scramblePassword(scramble []byte, password string) []byte {if len(password) == 0 {return nil}// stage1Hash = SHA1(password)crypt := sha1.New()crypt.Write([]byte(password))stage1 := crypt.Sum(nil)// scrambleHash = SHA1(scramble + SHA1(stage1Hash))// inner Hashcrypt.Reset()crypt.Write(stage1)hash := crypt.Sum(nil)// outer Hashcrypt.Reset()crypt.Write(scramble)crypt.Write(hash)scramble = crypt.Sum(nil)// token = scrambleHash XOR stage1Hashfor i := range scramble {scramble[i] ^= stage1[i]}return scramble}
根据源码可知，在认证时服务器发送的Greeting报文中包含Salt，而客户端收到Salt之后会使用SHA1算法将明文密码做2次SHA1，将结果与拼接Salt，再计算一次SHA1。
因此我们想在流量侧检测mysql弱口令，只能抓取salt值对弱口令字典生成相应的hash，再对比报文中的密码hash值，如果hash值一致我们就检测到了弱口令。
整个检测过程如图：
通过MySQL官方文档和我们抓取的pcap包，得到登录认证过程中的报文格式后，直接用zeek去跑流量，发现zeek的mysql.log日志中并没有salt值和password字段。
在查看zeek源码之后，我们可以知道zeek的内置协议解析器是用binpac这个开源组件编写的。我们只要修改mysql的协议解析器源码，让zeek在检测到mysql登录认证时，提取salt和password字段写入mysql.log日志就可以了。
首先编辑events.bif文件，在mysql_server_version事件的参数中增加salt参数。在mysql_handshake事件中增加password参数
event mysql_server_version%(c: connection, ver: string, salt: string%);event mysql_handshake%(c: connection, username: string, password: string%);
然后编辑mysql-protocol.pac文件，依据mysql数据包修改Handshake_v10的结构、Handshake_Response_Packet_v10的结构。
type Handshake_v10 = record {server_version : NUL_String;connection_id : uint32;auth_plugin_data_part_1: uint8[8];filler_1 : uint8;capability_flag_1 : uint16;character_set : uint8;status_flags : uint16;capability_flags_2 : uint16;auth_plugin_data_len : uint8;pad : padding[10];auth_plugin_data_part_2: uint8[12];filler_2 : uint8;auth_plugin_name : NUL_String;};type Handshake_Response_Packet_v10 = record {cap_flags : uint32;max_pkt_size : uint32;char_set : uint8;pad : padding[23];username : NUL_String;pad : padding[1];password : uint8[20];auth_plugin_name : NUL_String;connection_attributes : bytestring &restofdata;&let {deprecate_eof: bool = $context.connection.set_deprecate_eof(cap_flags & CLIENT_DEPRECATE_EOF);};
然后编辑mysql-analyzer.pac文件，修改处理mysql_server_version事件和mysql_handshake事件的函数逻辑。
function proc_mysql_initial_handshake_packet(msg: Initial_Handshake_Packet): bool%{if ( mysql_server_version ){if ( ${msg.version} == 10 ){std::string resultstring = zeek::util::fmt("%02x%02x%02x%02x%02x%02x%02x%02x""%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",${msg.handshake10.auth_plugin_data_part_1[0]},${msg.handshake10.auth_plugin_data_part_1[1]},${msg.handshake10.auth_plugin_data_part_1[2]},${msg.handshake10.auth_plugin_data_part_1[3]},${msg.handshake10.auth_plugin_data_part_1[4]},${msg.handshake10.auth_plugin_data_part_1[5]},${msg.handshake10.auth_plugin_data_part_1[6]},${msg.handshake10.auth_plugin_data_part_1[7]},${msg.handshake10.auth_plugin_data_part_2[0]},${msg.handshake10.auth_plugin_data_part_2[1]},${msg.handshake10.auth_plugin_data_part_2[2]},${msg.handshake10.auth_plugin_data_part_2[3]},${msg.handshake10.auth_plugin_data_part_2[4]},${msg.handshake10.auth_plugin_data_part_2[5]},${msg.handshake10.auth_plugin_data_part_2[6]},${msg.handshake10.auth_plugin_data_part_2[7]},${msg.handshake10.auth_plugin_data_part_2[8]},${msg.handshake10.auth_plugin_data_part_2[9]},${msg.handshake10.auth_plugin_data_part_2[10]},${msg.handshake10.auth_plugin_data_part_2[11]});zeek::BifEvent::enqueue_mysql_server_version(connection()->zeek_analyzer(),connection()->zeek_analyzer()->Conn(),zeek::make_intrusive<zeek::StringVal>(c_str(${msg.handshake10.server_version})),zeek::make_intrusive<zeek::StringVal>(resultstring));}if ( ${msg.version} == 9 )zeek::BifEvent::enqueue_mysql_server_version(connection()->zeek_analyzer(),connection()->zeek_analyzer()->Conn(),zeek::make_intrusive<zeek::StringVal>(c_str(${msg.handshake9.server_version})),zeek::make_intrusive<zeek::StringVal>(c_str(${msg.handshake9.scramble})));}return true;%}function proc_mysql_handshake_response_packet(msg: Handshake_Response_Packet): bool%{if ( ${msg.version} == 9 || ${msg.version == 10} )connection()->zeek_analyzer()->AnalyzerConfirmation();// If the client requested SSL and didn't provide credentials, switch to SSLif ( ${msg.version} == 10 && ( ${msg.v10_response.cap_flags} & CLIENT_SSL ) ){connection()->zeek_analyzer()->StartTLS();return true;}if ( mysql_handshake ){if ( ${msg.version} == 10 ){std::string resultstring = zeek::util::fmt("%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x""%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",${msg.v10_response.password[0]},${msg.v10_response.password[1]},${msg.v10_response.password[2]},${msg.v10_response.password[3]},${msg.v10_response.password[4]},${msg.v10_response.password[5]},${msg.v10_response.password[6]},${msg.v10_response.password[7]},${msg.v10_response.password[8]},${msg.v10_response.password[9]},${msg.v10_response.password[10]},${msg.v10_response.password[11]},${msg.v10_response.password[12]},${msg.v10_response.password[13]},${msg.v10_response.password[14]},${msg.v10_response.password[15]},${msg.v10_response.password[16]},${msg.v10_response.password[17]},${msg.v10_response.password[18]},${msg.v10_response.password[19]});zeek::BifEvent::enqueue_mysql_handshake(connection()->zeek_analyzer(),connection()->zeek_analyzer()->Conn(),zeek::make_intrusive<zeek::StringVal>(c_str(${msg.v10_response.username})),zeek::make_intrusive<zeek::StringVal>(resultstring));}if ( ${msg.version} == 9 )zeek::BifEvent::enqueue_mysql_handshake(connection()->zeek_analyzer(),connection()->zeek_analyzer()->Conn(),zeek::make_intrusive<zeek::StringVal>(c_str(${msg.v9_response.username})),zeek::make_intrusive<zeek::StringVal>(c_str(${msg.v9_response.password})));}return true;%}
最后根据自己的需要，修改mysql的zeek脚本，编译后重新部署zeek，就成功得到了mysql登录过程中的salt值和password值。
{"ts": 1713799007.950703,"uid": "CzJc2757Pq7acqSuc","id_orig_h": "10.x.x.x","id_orig_p": 51752,"id_resp_h": "10.x.x.x","id_resp_p": 3306,"cmd": "login","version": "5.7.30","salt": "326356*********a7f6b3b372f275135","username": "root","password": "1c889**********b089bff3dd","success": true,"rows": 0}
可以使用任意方式采集zeek的mysql.log日志（如：filebeat），写入消息队列（如kafka）。再写一个程序，读取消息队列，得到salt值和password的hash进行碰撞，就可以检测弱口令了。下面是一个demo
type ZeekMySQLLog struct {Ts float64 `json:"ts"`Uid string `json:"uid"`SrcIP string `json:"id_orig_h"`SrcPort int `json:"id_orig_p"`DstIP string `json:"id_resp_h"`DstPort int `json:"id_resp_p"`Cmd string `json:"cmd"`Arg string `json:"arg"`Version string `json:"version"`Salt string `json:"salt"`Username string `json:"username"`Password string `json:"password"`Success bool `json:"success"`Rows int `json:"rows"`}func checkPasswd(mysqlLog []byte) {var zeekLog ZeekMySQLLogerr := json.Unmarshal(mysqlLog, &zeekLog)if err != nil {logger.WithFields(logrus.Fields{"error": err}).Error("parse mysql log failed")return}if zeekLog.Cmd != "login" {//exclude non-login logreturn}if zeekLog.Success != true {//exclude login failed logreturn}salt := zeekLog.Saltpassword := zeekLog.Passwordscramble, err := hex.DecodeString(salt)if err != nil {logger.WithFields(logrus.Fields{"error": err, "salt": salt}).Error("decode salt failed")return}var knownpwd stringfor _, pwd := range checker.weakPasswdList {knownPwd := scramblePassword(scramble, pwd)if knownPwd == password {//detect weakpasswdknownpwd = pwdbreak}}if len(knownpwd) > 0 {fmt.Println(zeekLog)fmt.Println(knownpwd)return}}func initWeakPasswdList(filePath string) ([]string, error) {pwdFile, err := os.Open(filePath)if err != nil {return nil, fmt.Errorf("open %s failed: %v", filePath, err)}defer pwdFile.Close()var pwdList []stringscanner := bufio.NewScanner(pwdFile)for scanner.Scan() {pwdList = append(pwdList, scanner.Text())}if err = scanner.Err(); err != nil {return nil, fmt.Errorf("scan file failed: %v", err)}return pwdList, nil}func scramblePassword(scramble []byte, password string) string {if len(password) == 0 {return ""}// stage1Hash = SHA1(password)crypt := sha1.New()crypt.Write([]byte(password))stage1 := crypt.Sum(nil)// scrambleHash = SHA1(scramble + SHA1(stage1Hash))// inner Hashcrypt.Reset()crypt.Write(stage1)hash := crypt.Sum(nil)// outer Hashcrypt.Reset()crypt.Write(scramble)crypt.Write(hash)scramble = crypt.Sum(nil)// token = scrambleHash XOR stage1Hashfor i := range scramble {scramble[i] ^= stage1[i]}scrambleString := hex.EncodeToString(scramble)return scrambleString}
原文始发于微信公众号（Desync InfoSec）：Zeek使用与实践探索三
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