CVE-2021-33318: An Input Validation Vulnerability exists in Joel Christner .NET C# packages WatsonWebserver, IpMatcher 1.0.4.1

Q: How do I fix CVE-2021-33318?

ipmatcher: upgrade to newer than 1.0.4.1; watsonwebserver: upgrade to newer than 4.1.3. Exact commands for each OS are on this page.

Q: Is CVE-2021-33318 being exploited?

CVE-2021-33318 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-33318 affect?

CVE-2021-33318 affects ipmatcher, watsonwebserver. Severity is critical (CVSS 9.8). 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 aga

Q: How urgent is CVE-2021-33318?

Priority 65/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEUPGRADEUPGRADE

CVE-2021-33318 is a critical-severity flaw (CVSS 9.8) affecting ipmatcher, watsonwebserver. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.1% (top 19%)
CISA exploited list	No
Weakness	CWE-704
Published	2022-05-16
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: ipmatcher project · watsonwebserver project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-05-16 16:15 UTCPublished CVE record published
2026-06-17 03:54 UTCUpdated Record last modified

ipmatcher project ipmatcher UPGRADE

Affected: <= 1.0.4.1

Fixed in: newer than 1.0.4.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy ipmatcher || rpm -q ipmatcher || ipmatcher --version

2. UPGRADE to newer than 1.0.4.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade ipmatcher

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade ipmatcher

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

watsonwebserver project watsonwebserver UPGRADE

Affected: <= 4.1.3

Fixed in: newer than 4.1.3

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy watsonwebserver || rpm -q watsonwebserver || watsonwebserver --version

2. UPGRADE to newer than 4.1.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade watsonwebserver

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade watsonwebserver

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-33318?

ipmatcher: upgrade to newer than 1.0.4.1; watsonwebserver: upgrade to newer than 4.1.3. Exact commands for each OS are on this page.

Is CVE-2021-33318 being exploited?

CVE-2021-33318 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-33318 affect?

CVE-2021-33318 affects ipmatcher, watsonwebserver. Severity is critical (CVSS 9.8). 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 aga

How urgent is CVE-2021-33318?

Priority 65/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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