# CVE-2026-49336: @microsoft/kiota-http-fetchlibrary: Bearer token and Cookie leak across origin on redirect due to case-mismatched scrub in fetchRequestAdapter

> Attackers can steal Bearer tokens and Cookies via cross-origin redirects due to a case-sensitive header scrubbing bug in the default middleware chain.

- **Severity:** Medium 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jun 2026
- **Updated:** 22 Jun 2026
- **Also known as:** GHSA-396q-4vc8-28x9

## What is CVE-2026-49336?

CVE-2026-49336 is a medium-severity vulnerability in microsoft kiota-typescript, published on 19 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

@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.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor), CWE-178 (Improper Handling of Case Sensitivity)

## Which versions are affected by CVE-2026-49336?

2 open source packages ship an affected version, including @microsoft/kiota-http-fetchlibrary.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@microsoft/kiota-http-fetchlibrary` | npm | From 1.0.0-preview.97 | 1.0.0-preview.102 |
| `@microsoft/kiota-http-fetchlibrary` | npm | From 1.0.0-preview.97 | 1.0.0-preview.102 |

## How do I fix CVE-2026-49336?

Upgrade @microsoft/kiota-http-fetchlibrary to 1.0.0-preview.102 or later.

## Is CVE-2026-49336 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49336 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-49336 and fix it if it is affected.

What it is: CVE-2026-49336 is a medium-severity vulnerability in microsoft kiota-typescript, published on 19 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49336 exists.

Affected packages and fixed versions:
- @microsoft/kiota-http-fetchlibrary (npm): affected from 1.0.0-preview.97; fixed in 1.0.0-preview.102
- @microsoft/kiota-http-fetchlibrary (npm): affected from 1.0.0-preview.97; fixed in 1.0.0-preview.102

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-49336/ (Markdown: https://insights.sbomify.com/CVE-2026-49336/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-49336
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-49336
- OSV: https://osv.dev/vulnerability/CVE-2026-49336

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-49336/
Summaries are generated and may contain mistakes; the official description above is the record.