CVE-2021-27850
Severity CVSS v4.0:
Pending analysis
Type:
CWE-502
Deserialization of Untrusted Dat
Publication date:
15/04/2021
Last modified:
02/06/2021
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.
Impact
Base Score 3.x
9.80
Severity 3.x
CRITICAL
Base Score 2.0
10.00
Severity 2.0
HIGH
Vulnerable products and versions
| CPE | From | Up to |
|---|---|---|
| cpe:2.3:a:apache:tapestry:*:*:*:*:*:*:*:* | 5.4.0 (including) | 5.6.2 (excluding) |
| cpe:2.3:a:apache:tapestry:*:*:*:*:*:*:*:* | 5.7.0 (including) | 5.7.1 (excluding) |
To consult the complete list of CPE names with products and versions, see this page