# CVE-2026-66753: tiny-http 0.12.0 HTTP Response Splitting via Header Injection

> Attackers can inject CRLF bytes into HTTP headers in tiny-http, enabling response splitting, cache poisoning, and session fixation attacks.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 28 Jul 2026
- **Updated:** 14 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-66753, GHSA-5wm6-g4fr-88x8, UBUNTU-CVE-2026-66753

## What is CVE-2026-66753?

CVE-2026-66753 is a medium-severity vulnerability in tiny-http, published on 28 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

tiny-http through 0.12.0 contains an HTTP header injection vulnerability that allows attackers to inject carriage return (0x0D) and line feed (0x0A) bytes into HTTP header values on both request and response sides due to insufficient validation in header parsing and serialization. Attackers can exploit this injection primitive to perform response splitting, cache poisoning, session fixation via Set-Cookie injection, security header override, and request smuggling against line-feed-tolerant backends.

Weakness: CWE-113 (Improper Neutralization of CRLF Sequences in HTTP Headers)

## Which versions are affected by CVE-2026-66753?


## How do I fix CVE-2026-66753?

No fix has been published for CVE-2026-66753 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-66753 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-66753 exists.

Public exploit code:

- Security Advisory: HTTP Header Injection via Unvalidated CR and LF in Header Values (tiny_http) (github_poc): https://github.com/theopaid/CVE-2026-66753-HTTP-Header-Injection-via-Unvalidated-CR-and-LF-in-Header-Values-tiny_http-

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66753 and fix it if it is affected.

What it is: CVE-2026-66753 is a medium-severity vulnerability in tiny-http, published on 28 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-66753 exists.

Affected product: tiny-http. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-66753/ (Markdown: https://insights.sbomify.com/CVE-2026-66753/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66753
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66753
- OSV: https://osv.dev/vulnerability/CVE-2026-66753

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-66753/
Summaries are generated and may contain mistakes; the official description above is the record.