# CVE-2021-21294: Unbounded connection acceptance in http4s-blaze-server

Source: https://junglewise.ai/threats/cve-2021-21294-unbounded-connection-acceptance-in-http4s-blaze-server  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2021-02-02  
License: CC BY 4.0 with a link back

CVE-2021-21294 · Severity: low · CVSS 3.1 · Published 2021-02-02

Unbounded connection acceptance in http4s-blaze-server

Technologies: [org.http4s:http4s-blaze-server_2.13 (Maven)](https://junglewise.ai/threats/technologies/org-http4s-http4s-blaze-server-2-13). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven).

## Quick answers

**Is CVE-2021-21294 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2021-21294 being exploited in the wild.

**How severe is CVE-2021-21294?** Low severity, with a CVSS score of 3.1, published 2 February 2021.

**Which products and versions are affected?** org.http4s:http4s-blaze-server_2.12 (Maven) ECOSYSTEM:introduced=0,fixed=0.21.17; org.http4s:http4s-blaze-server_2.13 (Maven) ECOSYSTEM:introduced=0,fixed=0.21.17.

**Is there a fix for CVE-2021-21294?** Yes. org.http4s:http4s-blaze-server_2.12 (Maven): upgrade to 0.21.17 or later; org.http4s:http4s-blaze-server_2.13 (Maven): upgrade to 0.21.17 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2021-21294?** Check whether you run org.http4s:http4s-blaze-server_2.12 (Maven) or org.http4s:http4s-blaze-server_2.13 (Maven) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- org.http4s:http4s-blaze-server_2.12 (Maven): upgrade to 0.21.17 or later

  ```sh
  # set org.http4s:http4s-blaze-server_2.12 to 0.21.17 in your pom.xml or build.gradle
  ```

- org.http4s:http4s-blaze-server_2.13 (Maven): upgrade to 0.21.17 or later

  ```sh
  # set org.http4s:http4s-blaze-server_2.13 to 0.21.17 in your pom.xml or build.gradle
  ```


## Affected products

- org.http4s:http4s-blaze-server_2.12 (Maven) ECOSYSTEM:introduced=0,fixed=0.21.17
- org.http4s:http4s-blaze-server_2.13 (Maven) ECOSYSTEM:introduced=0,fixed=0.21.17

## Identifiers

- CVE-2021-21294
- GHSA-xhv5-w9c5-2r2w

## Related threats

- [http4s blaze HTTP/1.1 parser conformance bypass](https://junglewise.ai/threats/cve-2026-73494-http4s-blaze-http-1-1-parser-conformance-bypass)
- [Http4s blaze-server unbounded WebSocket message aggregation](https://junglewise.ai/threats/cve-2026-73493-http4s-blaze-server-unbounded-websocket-message-aggregation)