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MEDIUM severity

CVE-2021-23509 — json-ptr

MEDIUMFix: flitbit/json-ptr#42

CVE-2021-23509 is a medium-severity (CVSS 5.6) CWE-843 vulnerability in json-ptr. 2 public exploit references exist, so weaponization risk is real. A fix is available for json-ptr — see the affected versions and patch details below.

Prototype Pollution in json-ptr

Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
2 known
Exploitation data as of Oct 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs78th percentile — riskier than 78% of all scored CVEsHighest risk
1.25%1.61%1.97%2.33%1.7%1.8%Apr 26Aug 26Oct 26

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

How urgent is this, really

CVE-2021-23509 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.

json-ptrnpm
3.5Mdownloads / week

Description

This affects the package json-ptr before 3.0.0. A type confusion vulnerability can lead to a bypass of CVE-2020-7766 when the user-provided keys used in the pointer parameter are arrays.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmjson-ptrall versions3.0.0npm install json-ptr@3.0.0

Affected Products

1 product · 1 configurations
Application
json-ptrjson-ptr_project
< 3.0.0
range
Exploits & PoCs
2

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

This affects the package json-ptr before 3.0.0. A type confusion vulnera…

snyk.ioNVDNov 2021

This affects the package json-ptr before 3.0.0. A type confusion vulnera…

snyk.ioNVDNov 2021

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update json-ptr to 3.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23509 is resolved across your whole dependency graph.

  3. 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.

Frequently Asked Questions

This affects the package `json-ptr` before `3.0.0`. A type confusion vulnerability can lead to a bypass of CVE-2020-7766 when the user-provided keys used in the pointer parameter are arrays.
O3 Security · Impact-Aware SCA

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CVE-2021-23509: json-ptr — Fixed in 3.0.0