CVE-2026-44966Public exploitNetwork attack vector

Prototype pollution via unfiltered #set path assignment

Published May 26, 2026 · Updated May 26, 2026

Prototype pollution in Velocity.js 2.1.5 and earlier allows remote attackers to modify Object.prototype through crafted #set directives. The #set path-assignment logic in src/compile/set.ts writes arbitrary keys to base objects without blocking proto, constructor, or prototype traversal. Exploitation requires an application to render attacker-controlled templates; the resulting pollution supports process crashes or code execution only through environment-specific behavior.

CVSS severity8.3
High
EPSS probability0.55%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Prototype pollution in Velocity.js 2.1.5 and earlier allows remote attackers to modify Object.prototype through crafted #set directives. The #set path-assignment logic in src/compile/set.ts writes arbitrary keys to base objects without blocking proto, constructor, or prototype traversal. Exploitation requires an application to render attacker-controlled templates; the resulting pollution supports process crashes or code execution only through environment-specific behavior.

The record

CVE
CVE-2026-44966
Published
May 26, 2026
Updated
May 26, 2026
Vendor
shepherdwind
Product
Velocity.js
Classifications
CWE-1321, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 26, 2026CVE publishedPublication date reported by the CVE source.
  2. May 26, 2026Record 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=<= 2.1.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

shepherdwind · Velocity.jsversion=<= 2.1.5

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
8.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
T1190Exploit Public-Facing Application

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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