# CVE-2026-84380: HTTPX2: Conflicting Content-Length and Transfer-Encoding headers can be auto-generated

> HTTPX2 allows request smuggling via conflicting Content-Length and Transfer-Encoding headers, enabling desynchronization attacks against intermediaries.

- **Severity:** Medium 5.6 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 2 Sep 2026
- **Updated:** 2 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-84380, ECHO-6eae-343c-bdbc, GHSA-pf96-p4fj-6566, MINI-2chf-cvgf-w54r, MINI-qf3x-8j93-8pwv, PYSEC-2026-3849, UBUNTU-CVE-2026-84380

## What is CVE-2026-84380?

CVE-2026-84380 is a medium-severity vulnerability in pydantic httpx2, published on 2 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

HTTPX2 is a next generation HTTP client for Python. Prior to 2.11.0, Request._prepare() in src/httpx2/httpx2/_models.py can add a body-derived Content-Length header to a request that already contains a caller-supplied Transfer-Encoding header because its setdefault() processing checks each default header independently rather than treating the two framing headers as mutually exclusive. Fixed-size byte, JSON, form, and known-length multipart bodies can therefore be serialized over HTTP/1.1 with both headers, allowing request smuggling or connection desynchronization when downstream intermediaries disagree about which framing header takes precedence. This issue is fixed in version 2.11.0.

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

## Which versions are affected by CVE-2026-84380?

3 open source packages ship an affected version, including httpx2.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `httpx2` | PyPI | All versions | 2.11.0 |
| `httpx2` | PyPI | All versions | 2.11.0 |
| `httpx2` | PyPI | All versions | 2.11.0 |

## How do I fix CVE-2026-84380?

Upgrade httpx2 to 2.11.0 or later.

## Is CVE-2026-84380 being exploited?

There is no known exploitation of CVE-2026-84380 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-84380 and fix it if it is affected.

What it is: CVE-2026-84380 is a medium-severity vulnerability in pydantic httpx2, published on 2 Sep 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-2026-84380 in the wild and no public exploit code.

Affected packages and fixed versions:
- httpx2 (PyPI): affected all versions; fixed in 2.11.0
- httpx2 (PyPI): affected all versions; fixed in 2.11.0
- httpx2 (PyPI): affected all versions; fixed in 2.11.0

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-2026-84380/ (Markdown: https://insights.sbomify.com/CVE-2026-84380/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-84380
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-84380
- OSV: https://osv.dev/vulnerability/CVE-2026-84380

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-84380/
Summaries are generated and may contain mistakes; the official description above is the record.