CVE-2021-27850 Details

CVE-2021-27850

Published: 2021-04-15
Last Modified: 2021-06-02
CVE Author: NIST National Vulnerability Database
CVE Assigner: security@apache.org
Summary

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.

Analysis
Common Vulnerability Score System v2.0
Severity High
Base Score 10/10
Exploit Score 10/10
Access Vector Network
Access Complexity Low
Authentication None
Impact Score 10/10
Confidentiality Impact Complete
Availability Impact Complete
Integrity Impact Complete
Vector String AV:N/AC:L/Au:N/C:C/I:C/A:C
Common Vulnerability Score System v3.1
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
Vector String CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Products Reported
CPE Vulnerable Start Excluding
cpe:2.3:a:apache:tapestry:*:*:*:*:*:*:*:* Yes 5.4.0 5.6.2
cpe:2.3:a:apache:tapestry:*:*:*:*:*:*:*:* Yes 5.7.0 5.7.1
References

https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d
http://www.openwall.com/lists/oss-security/2021/04/15/1
https://security.netapp.com/advisory/ntap-20210528-0002/

CVE ID
CVE-2021-27850
Published
2021-04-15
Modified
2021-06-02
CVSSv2.0
High
CVSSv3.1
Critical
PCI Compliance
Fail
US-CERT Alert
No
CWE
CWE-502

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