CVE-2025-55164 — content-security-policy-p…
Fix: helmetjs/content-security-policy-parser@b13a525CVE-2025-55164 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.
content-security-policy-parser Prototype Pollution Vulnerability May Lead to RCE
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 CVE-2025-55164.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
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.
content-security-policy-parsernpmDescription
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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | content-security-policy-parser | all versions | 0.6.0npm install content-security-policy-parser@0.6.0 |
Detection & mitigation playbook
Open-source dependencyDetect
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.
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 CVE-2025-55164 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-55164 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-55164. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-55164 in your dependencies?
O3 Security finds CVE-2025-55164 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.