CVE-2021-33318

Name: CVE-2021-33318
Creator: NVD / NIST
Published: 2022-05-16T16:15:07.81+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 1.92%

Last modified Jun 17, 2026

CVE-2021-33318 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. 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.. EPSS estimates a 1.92% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

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

EPSS Probability

1.92%

77.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-704

Affected Software

Vendor	Product	Versions
Ipmatcher Project	Ipmatcher	<= 1.0.4.1
Watsonwebserver Project	Watsonwebserver	<= 4.1.3

References

https://github.com/jchristn/IpMatcherThird Party Advisory
https://github.com/jchristn/IpMatcher/commit/81d77c2f33aa912dbd032b34b9e184fc6e041d89Patch, Third Party Advisory
https://github.com/jchristn/WatsonWebserverThird Party Advisory
https://github.com/kaoudis/advisories/blob/main/0-2021.mdExploit, Third Party Advisory
https://github.com/jchristn/IpMatcherThird Party Advisory
https://github.com/jchristn/IpMatcher/commit/81d77c2f33aa912dbd032b34b9e184fc6e041d89Patch, Third Party Advisory
https://github.com/jchristn/WatsonWebserverThird Party Advisory
https://github.com/kaoudis/advisories/blob/main/0-2021.mdExploit, Third Party Advisory

Timeline

Published: May 16, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-33318?

How severe is CVE-2021-33318?

CVE-2021-33318 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 1.92% probability of exploitation in the next 30 days.

How do I fix CVE-2021-33318?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-33318?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST