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.NET
.NET NuGet
Not in CISA KEV
CRITICAL severity

Improper Input Validation in IpMatcherGHSA-qj93-37f5-mr29

CRITICALFix: jchristn/IpMatcher@81d77c2

GHSA-qj93-37f5-mr29 is a critical-severity (CVSS 9.8) CWE-704 vulnerability in IpMatcher. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for IpMatcher — see the affected versions and patch details below.

Also known asCVE-2021-33318
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
1 known
Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
2.1%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs81th percentile — riskier than 81% of all scored CVEsHighest risk
0.24%1.01%1.78%2.55%0.7%2.1%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

1 pkg affected
.NETIpMatcher

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.

Description

An Input Validation Vulnerability exists in Joel Christner .NET C# packages WatsonWebserver, IpMatcher 1.0.4.1 and below (IpMatcher) and 4.1.3 and below (WatsonWebserver) due to insufficient validation of input IP addresses and netmasks against the internal Matcher list of IP addresses and subnets.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
.NETNuGetIpMatcherall versions1.0.4.2dotnet add package IpMatcher --version 1.0.4.2

Affected Products

2 products · 2 configurations
Application
ipmatcheripmatcher_project
≤ 1.0.4.1
range
Application
watsonwebserverwatsonwebserver_project
≤ 4.1.3
range
Exploits & PoCs
1

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

An Input Validation Vulnerability exists in Joel Christner .NET C# packa…

github.comNVDMay 2022

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update IpMatcher to 1.0.4.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-qj93-37f5-mr29 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

An Input Validation Vulnerability exists in Joel Christner .NET C# packages WatsonWebserver, IpMatcher 1.0.4.1 and below (IpMatcher) and 4.1.3 and below (WatsonWebserver) due to insufficient validation of input IP addresses and netmasks against the internal Matcher list of IP addresses and subnets.
O3 Security · Impact-Aware SCA

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Improper Input Validation in IpMatcher (Critical 9.8)