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CVE-2021-33318

32
FAUCET Score

CVE-2021-33318 is an input validation vulnerability affecting Joel Christner's .NET C# packages WatsonWebserver (versions 4.1.3 and below) and IpMatcher (versions 1.0.4.1 and below). This flaw stems from insufficient validation of IP addresses and netmasks against internal matcher lists. It carries a critical CVSS score of 9.8, indicating a network-exploitable vulnerability with low attack complexity, requiring no user interaction, and potentially leading to complete compromise of confidentiality, integrity, and availability. While there is no evidence of active exploitation or public exploit code (Metasploit, Nuclei, ExploitDB), the vulnerability has garnered significant community discussion with 10 mentions.

Impacted Technologies

VendorProductVersion(s)CPE
<= 1.0.4.1CPE matchmatch criteria
cpe:2.3:a:ipmatcher_project:ipmatcher:*:*:*:*:*:*:*:*
<= 4.1.3CPE matchmatch criteria
cpe:2.3:a:watsonwebserver_project:watsonwebserver:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.8CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.96%
Probability of exploitation in next 30 days
EPSS Percentile
78.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0196 is in the 67th percentile among its peer group of 36,862 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (2)

github_advisorypatch availablevia nvd_reference
View patch
nugetpatch availablevia ghsa
Product: IpMatcherFixed in: 1.0.4.2

Vendor Advisories (1)

nugetGHSA-qj93-37f5-mr29critical

Improper Input Validation in IpMatcher

May 17, 2022

References

github.com / jchristn/IpMatcher
Third Party Advisory
github.com / jchristn/IpMatcher/commit/81d77c2f33aa912dbd032b34b9e184fc6e041d89
PatchThird Party Advisory
github.com / jchristn/WatsonWebserver
Third Party Advisory
github.com / kaoudis/advisories/blob/main/0-2021.md
ExploitThird Party Advisory