Vulnerability Details : CVE-2021-27850

Public exploit exists!
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.
Published 2021-04-15 08:15:15
Updated 2021-06-02 15:15:25
Source Apache Software Foundation
View at NVD,   CVE.org
Vulnerability category: Execute codeInformation leak

Exploit prediction scoring system (EPSS) score for CVE-2021-27850

Probability of exploitation activity in the next 30 days: 97.40%

Percentile, the proportion of vulnerabilities that are scored at or less: ~ 100 % EPSS Score History EPSS FAQ

Metasploit modules for CVE-2021-27850

  • Apache Tapestry HMAC secret key leak
    Disclosure Date: 2021-04-15
    First seen: 2021-07-22
    auxiliary/gather/cve_2021_27850_apache_tapestry_hmac_key
    This exploit finds the HMAC secret key used in Java serialization by Apache Tapestry. This key is located in the file AppModule.class by default and looks like the standard representation of UUID in hex digits (hd) : 6hd-4hd-4hd-4hd-12hd If the HMAC key has b

CVSS scores for CVE-2021-27850

Base Score Base Severity CVSS Vector Exploitability Score Impact Score Score Source
10.0
 HIGH AV:N/AC:L/Au:N/C:C/I:C/A:C
10.0
10.0
 NIST
9.8
 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.9
5.9
 NIST

CWE ids for CVE-2021-27850

References for CVE-2021-27850

Products affected by CVE-2021-27850

This web site uses cookies for managing your session, storing preferences, website analytics and additional purposes described in our privacy policy.
By using this web site you are agreeing to CVEdetails.com terms of use!
Accept Close