CVE-2025-55164Public exploitNetwork attack vector

Object prototype overwrite via __proto__ directive

Published Aug 12, 2025 · Updated Aug 20, 2025

Prototype pollution in Helmet.js content-security-policy-parser before 0.6.0 allows remote attackers to alter parsed object behavior. The parser stores untrusted directive names as properties on a normal JavaScript object, so a proto directive replaces the parsed result’s inherited prototype. Exposure requires a consuming application to pass attacker-controlled CSP text; no gadget exists in the library, so direct effects are property corruption and service interruption rather than standalone code execution.

CVSS severity8.8
High
EPSS probability0.42%
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 Helmet.js content-security-policy-parser before 0.6.0 allows remote attackers to alter parsed object behavior. The parser stores untrusted directive names as properties on a normal JavaScript object, so a proto directive replaces the parsed result’s inherited prototype. Exposure requires a consuming application to pass attacker-controlled CSP text; no gadget exists in the library, so direct effects are property corruption and service interruption rather than standalone code execution.

The record

CVE
CVE-2025-55164
Published
Aug 12, 2025
Updated
Aug 20, 2025
Vendor
Helmet.js
Product
content-security-policy-parser
Classifications
CWE-1321, T1190, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 12, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 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=< 0.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Helmet.js · content-security-policy-parserversion=< 0.6.0

Published CVSS scores

9.1GitLab Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
8.8GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N

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 exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
T1190Exploit Public-Facing Application
T1499.004Application or System Exploitation

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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