GHSA-mj8x-cpr8-x39h · Severity: critical · Ecosystem: maven — Remote code execution in Apache Tapestry
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.
Conclusion & alert: CVE-2021-27850 is rated High Exploit Risk (88.9/100): CVSS Critical severity, with high exploitation likelihood (EPSS 93.94%, 100th percentile). Core evidence: 1 public exploit reference(s) are indexed (Exploit-DB). Mandatory action: Public exploits are available—assess exposure, apply mitigations, and prioritize patching.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
| EDB-ID | Source | Kind | Published | Link |
|---|---|---|---|---|
| — | nvd_ref | exploit_tag | Exploit-DB ↗ |
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
| # | Date | Old EPSS score | New EPSS score | Delta (New - Old) |
|---|---|---|---|---|
| 1 | 2026-06-08 | 94.22% | 93.94% | -0.28% |
| 2 | 2025-11-21 | 93.35% | 94.22% | +0.87% |
| 3 | 2025-11-18 | — | 93.35% | — |
Full EPSS history (18 records total)
CVSS metrics for this CVE.
| Base score | Version | Severity | Vector | Exploitability | Impact | Score source |
|---|---|---|---|---|---|---|
| 9.8 | 3.1 | CRITICAL |
|
3.9 | 5.9 | [email protected] |
| 10.0 | 2.0 | HIGH |
|
10.0 | 10.0 | [email protected] |
GHSA-mj8x-cpr8-x39h · Severity: critical · Ecosystem: maven — Remote code execution in Apache Tapestry
| URL | Tags |
|---|---|
| http://www.openwall.com/lists/oss-security/2021/04/15/1 | Exploit Mailing List Third Party Advisory |
| https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3E | Mailing List Vendor Advisory |
| https://security.netapp.com/advisory/ntap-20210528-0002/ | Third Party Advisory |