Apache Critical Security Vulnerability — CVE-2021-27850

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Apache Critical Security Vulnerability — CVE-2021-27850

Apache released security updates for bypass of older vulnerability — Arbitrary Code Execution

Apache Tapestry — Arbitrary Code Execution Vulnerability

A critical unauthenticated remote code execution vulnerability was found all recent versions of Apache Tapestry.

In addition, The vulnerability I have found is a bypass of the fix for CVE-2019-0195.


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.

In addition, 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.

However, The fix for that bug was a blacklist filter that checks if the URL ends with `.class`, `.properties` or `.xml`.


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).

Affected Version

The affected versions include – Apache Tapestry 5.4.5, 5.5.0, 5.6.2 and 5.7.0.

Security Recommendation

Certainly, the solution for this vulnerability:

  • For Apache Tapestry 5.4.0 to 5.6.2, upgrade to 5.6.2 or later.
  • For Apache Tapestry 5.7.0, upgrade to 5.7.1 or later.

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By | 2021-04-16T22:27:07+05:30 April 16th, 2021|Security Update, Software Issues|

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