CVE-2021-33318

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.8 under NVD CVSS v3. EPSS exploit probability: 2.0%, top 22% 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
Trending — 3 sources updated this week
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.

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.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
49(Track)
EG Risk 49/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation2% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
78.2%
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.md
generic

GitHub - dotnet/WatsonWebserver: Watson is the fastest, easiest way to build scalable RESTful web servers and services in C#. · GitHub

https://github.com/jchristn/WatsonWebserver
github_commit

commit 81d77c2f33aa (jchristn/IpMatcher)

Fix landed in jchristn/IpMatcher commit 81d77c2f33aa — awaiting tagged release

https://github.com/jchristn/IpMatcher/commit/81d77c2f33aa912dbd032b34b9e184fc6e041d89
generic

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/IpMatcher

Affected Packages

(1 across 1 ecosystem)
NuGet(1)
PackageVulnerable rangeFixed inDependents
IpMatcher1.0.0, 1.0.1, 1.0.3, 1.0.4, 1.0.4.11.0.4.2—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 15× in last 7d / 47× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 101 total refreshes for this CVE.

  1. 2026-07-23 02:01 UTCEG score recompute
  2. 2026-07-22 22:48 UTCEG score recompute
  3. 2026-07-22 14:06 UTCEPSS rescore
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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 78.2% 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.

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