Async H1Application · Rust Lang
CVE-2020-26281
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedasync-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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceRequest smuggling vulnerability in async-h1 HTTP/1.1 parser where improper body handling causes the parser to read subsequent requests from within the body content at an offset. When a request body exceeds the buffer length, async-h1 incorrectly continues parsing from within the body instead of properly terminating, allowing attackers to smuggle requests through reverse proxies.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Async H1Application
< 2.3.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Locate async-h1 dependency in your projectSearch your Cargo.lock file for 'async-h1' and note the version number in the [[package]] section, or check your Cargo.toml for an explicit async-h1 dependencyAffected if The version listed is less than 2.3.0 (e.g., 2.2.0, 2.1.0, etc.)
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Identify indirect async-h1 usageRun 'cargo tree -i async-h1' to see which of your dependencies pull in async-h1 as a transitive dependency, then check the resolved version in Cargo.lockAffected if The resolved version is less than 2.3.0 regardless of direct or indirect usage
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Verify HTTP server implementation uses async-h1Check if your application uses HTTP server crates such as actix-web, tide, or other frameworks that rely on async-h1 for HTTP/1.1 parsing; review your Cargo.toml dependenciesAffected if Your HTTP handling stack includes async-h1 with a version below 2.3.0
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Confirm reverse proxy configurationInspect your deployment configuration (nginx, caddy, haproxy, or cloud proxy settings) to determine if requests pass through a reverse proxy before reaching your async-h1-based serverAffected if A reverse proxy forwards requests to your server and your async-h1 version is below 2.3.0
You are affected if your project resolves async-h1 to any version below 2.3.0 and uses it to handle HTTP/1.1 requests, especially when behind a reverse proxy.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data2.3.0
Upgrade async-h1 to version 2.3.0 or later; applications using this library should audit their dependency versions and test behind reverse proxies to confirm proper request handling.
Fix this in Async H1
Scoped from the published advisory
- Consultation2.0 h
- Implementation1.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,464.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-26281 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2020-26281 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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