CVE-2020-13936Public exploitNetwork attack vector

Code execution via incomplete class-hierarchy blocking

Published Mar 10, 2021 · Updated Feb 13, 2025

Sandbox bypass in Apache Velocity Engine 2.2 and earlier allows remote authenticated users to execute code through modified templates. SecureUberspector checks the concrete runtime class against its blocklist but fails to reject objects whose superclass or interface is blocked. Exploitation requires an application that lets untrusted users change Velocity templates; resulting code or commands run with the servlet-container account's privileges.

CVSS severity8.8
High
EPSS probability22.71%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Sandbox bypass in Apache Velocity Engine 2.2 and earlier allows remote authenticated users to execute code through modified templates. SecureUberspector checks the concrete runtime class against its blocklist but fails to reject objects whose superclass or interface is blocked. Exploitation requires an application that lets untrusted users change Velocity templates; resulting code or commands run with the servlet-container account's privileges.

The record

CVE
CVE-2020-13936
Published
Mar 10, 2021
Updated
Feb 13, 2025
Vendor
The Apache Software Foundation
Product
Apache Velocity Engine
Classifications
CWE-20, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 10, 2021CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=Apache Velocity Engine <=2.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

The Apache Software Foundation · Apache Velocity Engineversion=Apache Velocity Engine <=2.2

Published CVSS scores

8.8GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:L/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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
T1059.007JavaScript/JScript

Public exploit references

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

Technologies

Your stack

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Your stack

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