CVE-2026-48817 — starlette
MEDIUMCVE-2026-48817 is a medium-severity (CVSS 5.3) CWE-470 vulnerability in starlette. A fix is available for starlette — see the affected versions and patch details below.
Starlette: Arbitrary HTTP method dispatched to `HTTPEndpoint` attributes via `getattr`
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-48817.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-48817 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
starletteReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
When dispatching a request, HTTPEndpoint selects the handler by lowercasing the HTTP method and looking it up as an attribute with getattr, without restricting the lookup to a known set of HTTP verbs.
When an HTTPEndpoint subclass is registered through Route(...) without an explicit methods= argument, the route does not constrain the method and every method reaches the endpoint. If a non-standard HTTP method whose lowercased name matches an attribute on the endpoint subclass reaches the endpoint, that attribute is invoked as if it were a request handler. An attacker can use this to reach methods that were never meant to be HTTP handlers, such as internal helpers, without the authorization checks applied by the intended public handler.
Details
HTTPEndpoint uses the client-supplied method name to resolve an instance attribute, without validating it against the set of HTTP verbs the endpoint supports. A method such as _DO_DELETE therefore resolves an attribute like _do_delete and invokes it. Non-standard methods are valid RFC 9110 token methods, so an endpoint must not treat the method name as a trusted attribute selector.
Impact
An application is affected when all of the following hold:
- It defines an
HTTPEndpointsubclass and registers it viaRoute(...)without an explicitmethods=argument. - The subclass defines additional methods whose names match a non-standard HTTP-method token shape and that accept a single
requestargument and return a response.
This also affects frameworks built on Starlette, like FastAPI.
Mitigation
Register HTTPEndpoint subclasses with an explicit methods= argument on the Route, listing only the HTTP verbs the endpoint supports. The route then rejects any other method with 405 Method Not Allowed before it reaches the endpoint, so non-standard methods cannot resolve an attribute.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | starlette | all versions | 1.1.0pip install --upgrade 'starlette==1.1.0' |
Affected Products
starletteencodeDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for starlette, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update starlette to 1.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48817 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.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This is a Moderate impact flaw in Starlette, an ASGI framework, where an attacker can bypass authorization checks. By sending a specially crafted HTTP request with a non-standard method, an attacker can invoke internal methods not intended for public exposure. This vulnerability affects Red Hat products utilizing…
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.Source: Red Hat security advisory for CVE-2026-48817 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-48817 in your dependencies?
Find it across PyPI, including transitive dependencies.