CVE-2021-38512 is a high-severity (CVSS 7.5) CWE-444 vulnerability in actix-http. 1 public exploit reference exists, so weaponization risk is real. A fix is available for actix-http — see the affected versions and patch details below.
HTTP Request Smuggling in actix-http
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-38512 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
actix-httpReal-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
Affected versions of this crate did not properly detect invalid requests that could allow HTTP/1 request smuggling (HRS) attacks when running alongside a vulnerable front-end proxy server. This can result in leaked internal and/or user data, including credentials, when the front-end proxy is also vulnerable.
Popular front-end proxies and load balancers already mitigate HRS attacks so it is recommended that they are also kept up to date; check your specific set up. You should upgrade even if the front-end proxy receives exclusively HTTP/2 traffic and connects to the back-end using HTTP/1; several downgrade attacks are known that can also expose HRS vulnerabilities.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | actix-http | all versions | 2.2.1cargo update -p actix-http --precise 2.2.1 |
Affected Products
actix-httpactixfedorafedoraprojectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for actix-http, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update actix-http to 2.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-38512 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-2021-38512 in your dependencies?
Find it across crates.io, including transitive dependencies.