# CVE-2026-54387: Tinyproxy - HTTP Request Smuggling via CL/TE Desynchronization

> Attackers can desynchronize proxy and backend parsers via conflicting headers to inject requests, enabling cache poisoning and access control bypass.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/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:** Yes
- **Published:** 17 Jun 2026
- **Updated:** 14 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-54387, GHSA-9667-7p67-2364, UBUNTU-CVE-2026-54387

## What is CVE-2026-54387?

CVE-2026-54387 is a critical vulnerability in tinyproxy, published on 17 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Tinyproxy through 1.11.3, fixed in commit ff45d3b, fails to reconcile conflicting Content-Length and Transfer-Encoding: chunked headers, forwarding both verbatim to the backend while using Content-Length to determine how many request body bytes to consume. Remote attackers can desynchronize the proxy and backend parser state, allowing injection of arbitrary HTTP requests to the backend to enable cache poisoning, access control bypass, and request hijacking.

Weakness: CWE-444 (Inconsistent Interpretation of HTTP Requests)

## Which versions are affected by CVE-2026-54387?


## How do I fix CVE-2026-54387?

Apply the vendor's patch.

## Is CVE-2026-54387 being exploited?

There is no known exploitation of CVE-2026-54387 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54387 and fix it if it is affected.

What it is: CVE-2026-54387 is a critical vulnerability in tinyproxy, published on 17 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-54387 in the wild and no public exploit code.

Affected product: tinyproxy. 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-2026-54387/ (Markdown: https://insights.sbomify.com/CVE-2026-54387/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54387
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54387
- OSV: https://osv.dev/vulnerability/CVE-2026-54387

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54387/
Summaries are generated and may contain mistakes; the official description above is the record.