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MEDIUM severity

jszip Vulnerable to Prototype PollutionGHSA-jg8v-48h5-wgxg

MEDIUMFix: Stuk/jszip#766

GHSA-jg8v-48h5-wgxg is a medium-severity (CVSS 5.3) vulnerability in jszip. 3 public exploit or proof-of-concept references are indexed, so weaponization risk is real. A fix is available for jszip — see the affected versions and patch details below.

Also known asCVE-2021-23413
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
3 known
Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
3.4%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs89th percentile — riskier than 89% of all scored CVEsHighest risk
0.55%1.73%2.92%4.11%1.3%3.4%May 26Sep 26Nov 26

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs 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.

8Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream
jszipnpm
71.5Mdownloads / week

Description

This affects the package jszip before 3.7.0. Crafting a new zip file with filenames set to Object prototype values (e.g __proto__, toString, etc) results in a returned object with a modified prototype instance.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
📦npmjszip≥ 3.0.0&&< 3.7.03.7.0npm install jszip@3.7.0
📦npmjszipall versions2.7.0npm install jszip@2.7.0

Affected Products

1 product · 1 configurations
Application
jszipjszip_project
< 3.7.0
range
Exploits & PoCs
3

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

Detection & mitigation playbook

Open-source dependency
  1. Detect

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

  2. Fix

    Update jszip to 3.7.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-jg8v-48h5-wgxg 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 jszip before 3.7.0. Crafting a new zip file with filenames set to Object prototype values (e.g `__proto__`, `toString`, etc) results in a returned object with a modified prototype instance.
O3 Security · Impact-Aware SCA

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jszip Vulnerable to Prototype Pollution (Medium 5.3)