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CVE-2021-27850— Bypass of the fix for CVE-2019-0195

Quick assessment

Affected
Apache Software Foundation Apache Tapestry
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Apache Tapestry是美国阿帕奇（Apache）基金会的一款使用Java语言编写的Web应用程序框架。 Apache Tapestry 5.7.0, upgrade to 5.7.1 or later 存在安全漏洞，攻击者可利用该漏洞可以通过请求URL“http: localhost:8080 assets something services AppModule.class”下载文件“AppModule.class”，该URL包含一个HMAC密钥。

AI Predicted 9.8 Difficulty: Easy EPSS 93.47% · P100
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I. Basic Information for CVE-2021-27850

Vulnerability Information
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Vulnerability Title
Bypass of the fix for CVE-2019-0195
Source: CVE Program / CVE List V5
Vulnerability Description
A critical unauthenticated remote code execution vulnerability was found all recent versions of Apache Tapestry. The affected versions include 5.4.5, 5.5.0, 5.6.2 and 5.7.0. The vulnerability I have found is a bypass of the fix for CVE-2019-0195. Recap: Before the fix of CVE-2019-0195 it was possible to download arbitrary class files from the classpath by providing a crafted asset file URL. An attacker was able to download the file `AppModule.class` by requesting the URL `http://localhost:8080/assets/something/services/AppModule.class` which contains a HMAC secret key. The fix for that bug was a blacklist filter that checks if the URL ends with `.class`, `.properties` or `.xml`. Bypass: Unfortunately, the blacklist solution can simply be bypassed by appending a `/` at the end of the URL: `http://localhost:8080/assets/something/services/AppModule.class/` The slash is stripped after the blacklist check and the file `AppModule.class` is loaded into the response. This class usually contains the HMAC secret key which is used to sign serialized Java objects. With the knowledge of that key an attacker can sign a Java gadget chain that leads to RCE (e.g. CommonsBeanUtils1 from ysoserial). Solution for this vulnerability: * For Apache Tapestry 5.4.0 to 5.6.1, upgrade to 5.6.2 or later. * For Apache Tapestry 5.7.0, upgrade to 5.7.1 or later.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
信息暴露
Source: CVE Program / CVE List V5
Vulnerability Title
Apache Tapestry 代码问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Apache Tapestry是美国阿帕奇（Apache）基金会的一款使用Java语言编写的Web应用程序框架。 Apache Tapestry 5.7.0, upgrade to 5.7.1 or later 存在安全漏洞，攻击者可利用该漏洞可以通过请求URL“http: localhost:8080 assets something services AppModule.class”下载文件“AppModule.class”，该URL包含一个HMAC密钥。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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Affected Products

Vendor Product Affected Versions CPE Subscribe
Apache Software Foundation Apache Tapestry Apache Tapestry 5.5.0 -

II. Public POCs for CVE-2021-27850

# POC Description Source Link Shenlong Link
1 A Proof of concept for CVE-2021-27850 affecting Apache Tapestry and leading to unauthencticated remote code execution. https://github.com/kahla-sec/CVE-2021-27850_POC POC Details
2 A Proof of concept for CVE-2021-27850 affecting Apache Tapestry and leading to unauthencticated remote code execution. https://github.com/dorkerdevil/CVE-2021-27850_POC POC Details
3 Apache Tapestry CVE-2021-27850 PoC https://github.com/Ovi3/CVE_2021_27850_POC POC Details
4 CVE-2021-27850 ysoserial https://github.com/novysodope/CVE-2021-27850 POC Details
5 Apache Tapestry contains a critical unauthenticated remote code execution vulnerability. Affected versions include 5.4.5, 5.5.0, 5.6.2 and 5.7.0. Note that this vulnerability is a bypass of the fix for CVE-2019-0195. Before that fix it was possible to download arbitrary class files from the classpath by providing a crafted asset file URL. https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-27850.yaml POC Details
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III. Intelligence Information for CVE-2021-27850

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Vendor Advisories for CVE-2021-27850 (1)

Mailing List Discussions for CVE-2021-27850 (2)

IV. Related Vulnerabilities

Same product: Apache Tapestry
Same vendor: Apache Software Foundation
Same weakness: CWE-200

V. Comments for CVE-2021-27850

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