# CVE-2020-26281: request smuggling in async-h1

> Attackers can smuggle HTTP requests to forge headers or capture other users' data in Rust web servers using async-h1 behind a reverse proxy.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 Dec 2020
- **Updated:** 4 Aug 2024

## What is CVE-2020-26281?

CVE-2020-26281 is a medium-severity vulnerability in http-rs async-h1, published on 21 Dec 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

async-h1 is an asynchronous HTTP/1.1 parser for Rust (crates.io). There is a request smuggling vulnerability in async-h1 before version 2.3.0. This vulnerability affects any webserver that uses async-h1 behind a reverse proxy, including all such Tide applications. If the server does not read the body of a request which is longer than some buffer length, async-h1 will attempt to read a subsequent request from the body content starting at that offset into the body. One way to exploit this vulnerability would be for an adversary to craft a request such that the body contains a request that would not be noticed by a reverse proxy, allowing it to forge forwarded/x-forwarded headers. If an application trusted the authenticity of these headers, it could be misled by the smuggled request. Another potential concern with this vulnerability is that if a reverse proxy is sending multiple http clients' requests along the same keep-alive connection, it would be possible for the smuggled request to specify a long content and capture another user's request in its body. This content could be captured in a post request to an endpoint that allows the content to be subsequently retrieved by the adversary. This has been addressed in async-h1 2.3.0 and previous versions have been yanked.

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

## Which versions are affected by CVE-2020-26281?

It affects 1 product.


Products: Rust-Lang Async-H1.

## How do I fix CVE-2020-26281?

Upgrade to a fixed version.

## Is CVE-2020-26281 being exploited?

There is no known exploitation of CVE-2020-26281 in the wild and no public exploit code.

## Other vulnerabilities in http-rs async-h1

- [CVE-2020-36202](https://insights.sbomify.com/CVE-2020-36202/): Other in n/a (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-26281 and fix it if it is affected.

What it is: CVE-2020-26281 is a medium-severity vulnerability in http-rs async-h1, published on 21 Dec 2020. 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-2020-26281 in the wild and no public exploit code.

Affected product: http-rs async-h1. 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-2020-26281/ (Markdown: https://insights.sbomify.com/CVE-2020-26281/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-26281
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-26281
- OSV: https://osv.dev/vulnerability/CVE-2020-26281

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-26281/
Summaries are generated and may contain mistakes; the official description above is the record.