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CVE-2021-27850

CVE information

Published

1 year ago

Last Modified

1 year ago

CVSSv2.0 Severity

High

CVSSv3.1 Severity

Critical

Impact Analysis

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..

CVSSv2.0 Score

Severity
High
Base Score
10/10
Exploit Score
10/10
Access Vector
Network
Access Complexity
Low
Authentication Required
None
Impact Score
10/10
Confidentiality Impact
Complete
Availability Impact
Complete
Integrity Impact
Complete

CVSSv3.1 Score

Severity
Critical
Base Score
9.8/10
Exploit Score
3.9/10
Access Vector
Network
Access Complexity
Low
Privileges Required
None
Impact Score
5.9/10
Confidentiality Impact
High
Availability Impact
High
Integrity Impact
High
Scope
Unchanged
User Interaction
None

Products Affected

CPE Affected Vulnerable Excluding Edit
cpe:2.3:a:apache:tapestry:*:*:*:*:*:*:*:*
  Yes
5.7.0 5.7.1
cpe:2.3:a:apache:tapestry:*:*:*:*:*:*:*:*
  Yes
5.4.0 5.6.2