# CVE-2026-66753: tiny-http HTTP header injection in header parsing and serialization

Source: https://junglewise.ai/threats/cve-2026-66753-tiny-http-http-header-injection-in-header-parsing-and  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-28. Updated: 2026-07-28  
License: CC BY 4.0 with a link back

CVE-2026-66753 · Severity: medium · CVSS 5.3 · Published 2026-07-28

tiny-http is a lightweight library used by developers to build web servers. A security flaw allows attackers to manipulate the technical headers sent between the server and the user. This could be used to trick web browsers into performing unintended actions, such as stealing user sessions, bypassing security settings, or poisoning web caches to serve malicious content to other users.

Technologies: [Tiny-Http](https://junglewise.ai/threats/technologies/tiny-http). Vendors: [Tiny-Http](https://junglewise.ai/threats/vendors/tiny-http).

## Quick answers

**Is CVE-2026-66753 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-66753 being exploited in the wild.

**How severe is CVE-2026-66753?** Medium severity, with a CVSS score of 5.3, published 28 July 2026.

**Which products and versions are affected?** Tiny-Http through 0.12.0.

**Is there a fix for CVE-2026-66753?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-66753 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-66753?** Check whether you run Tiny-Http 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

A CRLF injection vulnerability (CWE-113) exists in tiny-http through version 0.12.0 due to insufficient validation of header values during parsing and serialization. An unauthenticated remote attacker can inject 0x0D (CR) and 0x0A (LF) bytes into both request and response headers. This primitive can be leveraged to perform HTTP response splitting, cache poisoning, session fixation via Set-Cookie injection, and request smuggling against backends that are tolerant of line-feed characters. The vulnerability affects both the client-facing and backend-facing sides of the library's header handling.

## Affected products

- tiny-http tiny-http through 0.12.0

## Timeline

- 2026-07-28: disclosed
- 2026-07-28: advisory

## References

- [https://github.com/theopaid/HTTP-Header-Injection-via-Unvalidated-CR-and-LF-in-Header-Values-tiny_http-/tree/master](https://github.com/theopaid/HTTP-Header-Injection-via-Unvalidated-CR-and-LF-in-Header-Values-tiny_http-/tree/master)
- [https://www.vulncheck.com/advisories/tiny-http-http-response-splitting-via-header-injection](https://www.vulncheck.com/advisories/tiny-http-http-response-splitting-via-header-injection)

## Related threats

- [tiny-http HTTP request smuggling via Transfer-Encoding handling](https://junglewise.ai/threats/cve-2026-66752-tiny-http-http-request-smuggling-via-transfer-encoding-handling)
- [tiny-http directory traversal](https://junglewise.ai/threats/cve-2017-16097-tiny-http-directory-traversal)