CVE-2020-26281 — async-h1
HIGHCVE-2020-26281 is a high-severity (CVSS 7.5) CWE-444 vulnerability in async-h1. A fix is available for async-h1 — see the affected versions and patch details below.
Async-h1 request smuggling possible with long unread bodies
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-26281 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
async-h1Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Impact
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.
Patches
This has been addressed in async-h1 2.3.0 and previous versions have been yanked.
Workarounds
none
References
https://github.com/http-rs/async-h1/releases/tag/v2.3.0
For more information
If you have any questions or comments about this advisory:
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | async-h1 | all versions | 2.3.0cargo update -p async-h1 --precise 2.3.0 |
Affected Products
async-h1rust-langDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for async-h1, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update async-h1 to 2.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-26281 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2020-26281 in your dependencies?
Find it across crates.io, including transitive dependencies.