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CVE-2021-21328

19
FAUCET Score

CVE-2021-21328 is a denial-of-service (DoS) vulnerability affecting Vapor, a Swift web framework, specifically versions prior to 4.40.1. An unauthenticated attacker can exhaust system resources by sending numerous requests with unique paths, leading to the creation of unlimited counters and timers when a metrics backend is bootstrapped. This medium-severity vulnerability (CVSS 5.3) has a low attack complexity and can cause service disruption, potentially impacting downstream services. There is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 4.40.1CPE matchmatch criteria
cpe:2.3:a:vapor_project:vapor:*:*:*:*:*:swift:*:*

CVSS Data

CVSS version used by this source: 3.1

5.3MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
LOW
Exploitability Score
3.9
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.63%
Probability of exploitation in next 30 days
EPSS Percentile
73.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0163 is in the 58th percentile among its peer group of 23,723 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 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
swiftpatch availablevia ghsa
Product: github.com/vapor/vaporFixed in: 4.40.1

Vendor Advisories (1)

swiftGHSA-gcj9-jj38-hwmcmedium

Vapor's Metrics integration could cause a system drain

Jun 9, 2023

References

github.com / vapor/vapor/commit/e3aa712508db2854ac0ab905696c65fd88fa7e23
PatchThird Party Advisory
github.com / vapor/vapor/releases/tag/4.40.1
Release NotesThird Party Advisory
github.com / vapor/vapor/security/advisories/GHSA-gcj9-jj38-hwmc
Third Party Advisory
vapor.codes
Product