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.
CVE-2021-33318
CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence
This critical-severity CVE scores 9.8 under NVD CVSS v3. EPSS exploit probability: 0.7%, top 27% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
Triggered by: NVD CVSS baseline
Sources: epss, nvd
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 2%CVSS: 9.8Exploit: NoneExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 9.8
- EG Score
- 9.8(medium)
- EPSS
- 78.0%
- KEV
- Not listed
Published
May 16, 2022
Last Modified
November 21, 2024
Advisory Details (4)
Auto-updated Jun 12, 2026🔬 Proof of concept available. Upstream fix merged — awaiting tagged release. Sources: github_commit.
generic🟡 PoC Available
advisories/0-2021.md at main · kaoudis/advisories · GitHub
https://github.com/kaoudis/advisories/blob/main/0-2021.mdgeneric
GitHub - dotnet/WatsonWebserver: Watson is the fastest, easiest way to build scalable RESTful web servers and services in C#. · GitHub
https://github.com/jchristn/WatsonWebservergithub_commit
commit 81d77c2f33aa (jchristn/IpMatcher)
Fix landed in jchristn/IpMatcher commit 81d77c2f33aa — awaiting tagged release
https://github.com/jchristn/IpMatcher/commit/81d77c2f33aa912dbd032b34b9e184fc6e041d89generic
GitHub - jchristn/IpMatcher: C# library for maintaining a match list of IP addresses and networks and comparing inputs to see if a match exists. · GitHub
https://github.com/jchristn/IpMatcherAffected Packages
(1 across 1 ecosystem)
NuGet(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| IpMatcher | 1.0.0, 1.0.1, 1.0.3, 1.0.4, 1.0.4.1 | 1.0.4.2 | — |
Frequently asked(5)
What is CVE-2021-33318?
CVE-2021-33318 is a critical vulnerability published on May 16, 2022. 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.
When was CVE-2021-33318 disclosed?
CVE-2021-33318 was first published in the National Vulnerability Database on May 16, 2022, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-33318 actively exploited?
CVE-2021-33318 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 78.0% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-33318?
CVE-2021-33318 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-33318?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-33318, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-33318
Is Your Infrastructure Affected by CVE-2021-33318?
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