# CVE-2026-69211: Http4s ResponseCookie header injection via unescaped attributes

Source: https://junglewise.ai/threats/cve-2026-69211-http4s-responsecookie-header-injection-via-unescaped-attributes  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-15. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-69211 · Severity: medium · CVSS 4.8 · Published 2026-09-15

Http4s is a Scala web framework library that handles HTTP cookie responses. The ResponseCookie.render function fails to properly escape cookie attribute values from untrusted input, allowing attackers to inject additional cookie attributes (such as Domain or SameSite) or control characters that could enable header splitting attacks. This can broaden cookie exposure scope or bypass security protections in web applications using the library.

Technologies: [Http4s](https://junglewise.ai/threats/technologies/http4s). Vendors: [Http4s](https://junglewise.ai/threats/vendors/http4s).

## Quick answers

**Is CVE-2026-69211 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-69211 being exploited in the wild.

**How severe is CVE-2026-69211?** Medium severity, with a CVSS score of 4.8, published 15 September 2026.

**Which products and versions are affected?** Http4s prior to 0.23.35 and 1.0.0-M47.

**Is there a fix for CVE-2026-69211?** A patch was published on 2025-07-06: Version 0.23.35 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-69211 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-69211?** Check whether you run Http4s 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.

## Technical details

The vulnerability is a header injection flaw in the ResponseCookie.render method. The vulnerable component fails to sanitize semicolons and control characters from cookie name, content, domain, path, and extension fields before rendering them into HTTP Set-Cookie headers. An attacker who controls cookie input can inject semicolons to add arbitrary cookie attributes (e.g., Domain=attacker.com) or embed control characters to enable CRLF header splitting on permissive HTTP backends. The fix strips all control characters from all five fields and removes semicolons from name, content, domain, and path while preserving extension delimiter behavior. Patches are available in versions 0.23.35 and 1.0.0-M47.

## Affected products

- http4s http4s prior to 0.23.35 and 1.0.0-M47

## Timeline

- 2026-09-15: disclosed
- 2025-07-06: patched: Version 0.23.35 released

## References

- [https://github.com/http4s/http4s/commit/5c8e69ac0f4a2fe03c3481dccd74101cd2e2a890](https://github.com/http4s/http4s/commit/5c8e69ac0f4a2fe03c3481dccd74101cd2e2a890)
- [https://github.com/http4s/http4s/releases/tag/v0.23.35](https://github.com/http4s/http4s/releases/tag/v0.23.35)

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