CVE-2021-27850 Detail

Current 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.


View Analysis Description

Severity



CVSS 3.x Severity and Metrics:

NIST CVSS score
NIST: NVD
Base Score:  9.8 CRITICAL
Vector:  CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H


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Note: NVD Analysts have published a CVSS score for this CVE based on publicly available information at the time of analysis. The CNA has not provided a score within the CVE List.

References to Advisories, Solutions, and Tools

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Hyperlink Resource
http://www.openwall.com/lists/oss-security/2021/04/15/1 Exploit  Mailing List  Third Party Advisory 
https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3E Mailing List  Vendor Advisory 

Weakness Enumeration

CWE-ID CWE Name Source
CWE-502 Deserialization of Untrusted Data cwe source acceptance level NIST   Contributor acceptance level Apache Software Foundation  
CWE-200 Exposure of Sensitive Information to an Unauthorized Actor Contributor acceptance level Apache Software Foundation  

Known Affected Software Configurations Switch to CPE 2.2

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Change History

2 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2021-27850
NVD Published Date:
04/15/2021
NVD Last Modified:
04/22/2021
Source:
Apache Software Foundation