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content-security-policy-parser Prototype Pollution Vulnerability May Lead to RCEGHSA-w2cq-g8g3-gm83

Fix: helmetjs/content-security-policy-parser@b13a525

GHSA-w2cq-g8g3-gm83 is a CWE-1321 vulnerability in content-security-policy-parser. A fix is available for content-security-policy-parser — see the affected versions and patch details below.

Also known asCVE-2025-55164
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-w2cq-g8g3-gm83.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk+0.03%
Lower risk than most CVEs41th percentile — riskier than 41% of all scored CVEsHighest risk
0.00%0.32%0.65%0.97%0.2%0.5%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

27other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
content-security-policy-parsernpm
686Kdownloads / week

Description

Impact

A prototype pollution vulnerability exists in versions 0.5.0 and earlier, wherein if you provide a policy name called __proto__ you can override the Object prototype.

For example:

const parse = require('content-security-policy-parser');

const x = parse("default-src 'self'; __proto__ foobar");
console.log('raw print:', x);
console.log('toString:', x.toString());

Outputs:

raw print: Array { 'default-src': [ "'self'" ] }
toString: foobar

Whilst no gadget exists in this library, it is possible via other libraries expose functionality that enable RCE. It is customary to label prototype pollution vulnerabilities in this way. The most common effect of this is denial of service, as you can trivially overwrite properties.

As the content security policy is provided in HTTP queries, it is incredibly likely that network exploitation is possible.

Patches

There has been a patch implemented a year ago (11 Feb 2024), but low uptake of patched versions has not been observed in the wild - only 17% of weekly downloads are of patched versions.

Workarounds

By disabling prototype method in NodeJS you can neutralise all possible prototype pollution attacks. Provide either --disable-proto=delete (recommended) or --disable-proto=throw as an argument to node to enable this feature.

References

Issue revealing the problem, January 26 2024 Commit fixing the problem

Credit to @EvanHahn for patching the vulnerability promptly, and @pnappa (Patrick Nappa) for discovery.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmcontent-security-policy-parserall versions0.6.0npm install content-security-policy-parser@0.6.0

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for content-security-policy-parser, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update content-security-policy-parser to 0.6.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-w2cq-g8g3-gm83 is resolved across your whole dependency graph.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### Impact A prototype pollution vulnerability exists in versions 0.5.0 and earlier, wherein if you provide a policy name called `__proto__` you can override the Object prototype. For example: ``` const parse = require('content-security-policy-parser'); const x = parse("default-src 'self'; __proto__ foobar"); console.log('raw print:', x); console.log('toString:', x.toString()); ``` Outputs: ``` raw print: Array { 'default-src': [ "'self'" ] } toString: foobar ``` Whilst no gadget exists in this library, it is possible via other libraries expose functionality that enable RCE. It is custom
O3 Security · Impact-Aware SCA

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