@microsoft/kiota-http-fetchlibrary: Bearer token and Cookie leak across origin on redirect due to case-mismatched scrub in fetchRequestAdapter

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.5 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:P · score source

EPSS

• CVE-2026-49336: 0.75% estimated exploitation activity in the next 30 days; percentile 54.92 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary @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. Affected versions @microsoft/kiota-http-fetchlibrary = 1.0.0-preview.97…

Published by the source

26 Jun 2026, 22:23 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:56 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-396q-4vc8-28x9

2. Revision 2 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-396q-4vc8-28x9

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# Patch Next advisory brief: CVE-2026-49336

Advisory: @microsoft/kiota-http-fetchlibrary: Bearer token and Cookie leak across origin on redirect due to case-mismatched scrub in fetchRequestAdapter
IDs: CVE-2026-49336, GHSA-396q-4vc8-28x9
Record: https://patchnext.com/advisories/cve-2026-49336 (revision 3, source checked 26 Oct 2026, 12:56 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @microsoft/kiota-http-fetchlibrary 1.0.0-preview.102. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @microsoft/kiota-http-fetchlibrary: affected >= 1.0.0-preview.97, <= 1.0.0-preview.101; fixed in 1.0.0-preview.102

## Suggested inspection (read-only)
- `npm ls @microsoft/kiota-http-fetchlibrary --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @microsoft/kiota-http-fetchlibrary.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-396q-4vc8-28x9 (OSV record GHSA-396q-4vc8-28x9 lists affected ranges: npm @microsoft/kiota-http-fetchlibrary >=1.0.0-preview.97 <1.0.0-preview.102 (fixed))
- Verified: https://github.com/advisories/GHSA-396q-4vc8-28x9 (GitHub-reviewed advisory GHSA-396q-4vc8-28x9 lists affected ranges: npm @microsoft/kiota-http-fetchlibrary >=1.0.0-preview.97 <=1.0.0-preview.101)

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