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CVE-2021-27850
CVE information
Published
Last Modified
CVSSv2.0 Severity
CVSSv3.1 Severity
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 |