CVE-2021-27850Known exploitationPublic exploitNetwork attack vector

Unauthenticated code execution via classpath filter bypass

Published Apr 15, 2021 · Updated Aug 3, 2024

Deserialization in Apache Tapestry 5.4.0 through 5.6.2 and 5.7.0 allows remote attackers to execute arbitrary code via HTTP. ClasspathAssetRequestHandler checks an asset path against an extension blocklist before normalization, so a trailing slash exposes AppModule.class and its HMAC key. The leaked key lets unauthenticated attackers sign a Java gadget chain that the server accepts, granting code execution in the web application process.

CVSS severity9.8
Critical
EPSS probability93.47%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Deserialization in Apache Tapestry 5.4.0 through 5.6.2 and 5.7.0 allows remote attackers to execute arbitrary code via HTTP. ClasspathAssetRequestHandler checks an asset path against an extension blocklist before normalization, so a trailing slash exposes AppModule.class and its HMAC key. The leaked key lets unauthenticated attackers sign a Java gadget chain that the server accepts, granting code execution in the web application process.

The record

CVE
CVE-2021-27850
Published
Apr 15, 2021
Updated
Aug 3, 2024
Vendor
The Apache Software Foundation
Product
Apache Tapestry
Classifications
CWE-922, CWE-502, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Apache Tapestry 5.4.5 <Apache Tapestry 5.4.0*
  2. Affected versionversion=Apache Tapestry 5.5.0
  3. Affected versionversion=Apache Tapestry 5.6.2 <Apache Tapestry 5.6.0*
  4. Affected versionversion=Apache Tapestry 5.7.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Tapestryversion=Apache Tapestry 5.4.5 <Apache Tapestry 5.4.0*; version=Apache Tapestry 5.5.0; version=Apache Tapestry 5.6.2 <Apache Tapestry 5.6.0*; version=Apache Tapestry 5.7.0

Published CVSS scores

9.8OSVCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-922Insecure Storage of Sensitive Information
CWE-502Deserialization of Untrusted Data
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo