Medium
Security advisory
Vapor is a web framework for Swift. In Vapor before version 4.40.1, there is a DoS attack against anyone who Bootstraps a metrics backend for their Vapor app. The following is the attack vector: 1. send unlimited requests against a vapor instance with different paths. this will create unlimited counters and timers, which will eventually drain the system. 2. downstream services might suffer from this attack as well by being spammed with error paths. This has been patched in 4.40.1. The `DefaultResponder` will rewrite any undefined route paths for to `vapor_route_undefined` to avoid unlimited counters.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2021-21328
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 11:14 UTC · Revision 1
Source evidence
Vapor is a web framework for Swift. In Vapor before version 4.40.1, there is a DoS attack against anyone who Bootstraps a metrics backend for their Vapor app. The following is the attack vector: 1. send unlimited requests against a vapor instance with different paths. this will create unlimited counters and timers, which will eventually drain the system. 2. downstream services might suffer from this attack as well by being spammed with error paths. This has been patched in 4.40.1. The `DefaultResponder` will rewrite any undefined route paths for to `vapor_route_undefined` to avoid unlimited counters.
osv:CVE-2021-21328
Complete source record
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"url": "https://osv.dev/vulnerability/CVE-2021-21328",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "CVE-2021-21328",
"summary": "Vapor is a web framework for Swift. In Vapor before version 4.40.1, there is a DoS attack against anyone who Bootstraps a metrics backend for their Vapor app. The following is the attack vector: 1. send unlimited requests against a vapor instance with different paths. this will create unlimited counters and timers, which will eventually drain the system. 2. downstream services might suffer from this attack as well by being spammed with error paths. This has been patched in 4.40.1. The `DefaultResponder` will rewrite any undefined route paths for to `vapor_route_undefined` to avoid unlimited counters.",
"evidence": "osv:CVE-2021-21328",
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"modified": "2026-10-20T10:53:33.645626180Z",
"provider": "osv",
"references": [
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"evidence": "/id"
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"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 384421,
"published_at": "2021-02-26T02:15:12.713+00:00"
}