CVE-2026-49336
@microsoft/kiota-http-fetchlibrary: Bearer token and Cookie leak across origin on redirect due to case-mismatched scrub in fetchRequestAdapter
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
@microsoft/kiota-http-fetchlibrarynpmDescription
@microsoft/kiota-http-fetchlibrary provides TypeScript libraries for Kiota-generated API clients. In versions 1.0.0-preview.97 through 1.0.0-preview.101, @microsoft/kiota-http-fetchlibrary's RedirectHandler is documented as stripping Authorization and Cookie from cross-origin redirect targets, but the default scrubSensitiveHeaders callback in RedirectHandlerOptions uses case-sensitive property deletion (delete headers.Authorization, delete headers.Cookie) on a headers object that FetchRequestAdapter.getRequestFromRequestInformation has already lower-cased. The delete therefore targets keys that do not exist, the scrub is a no-op, and any Bearer token or Cookie attached by a kiota-generated SDK is forwarded to an attacker-controlled host across a 30x redirect. This is reachable in the default middleware chain (MiddlewareFactory.getDefaultMiddlewares) with no custom configuration, and applies to every kiota-generated TypeScript SDK that uses BaseBearerTokenAuthenticationProvider or any other authentication provider that sets the Authorization request header. Version 1.0.0-preview.102 patches the issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @microsoft/kiota-http-fetchlibrary | ≥ 1.0.0-preview.97&&< 1.0.0-preview.102 | 1.0.0-preview.102 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @microsoft/kiota-http-fetchlibrary. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update @microsoft/kiota-http-fetchlibrary to 1.0.0-preview.102 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-49336 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.
How O3 protects you
O3 pinpoints whether CVE-2026-49336 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-49336. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-49336 in your dependencies?
O3 detects CVE-2026-49336 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.