---
id: CVE-2026-48595
aliases:
  - GHSA-9m9w-gxf7-rh8m
title: >-
  Tesla: Authorization header leaks on cross-origin redirect via case-sensitive
  filtering
summary: >-
  Tesla: Authorization header leaks on cross-origin redirect via case-sensitive
  filtering
severity: high
cwe:
  - CWE-178
vendor: tesla
product: tesla
ecosystem: erlang
affected:
  - 'tesla >= 0.6.0, < 1.18.3'
patched:
  - tesla 1.18.3
published: '2026-07-10'
updated: '2026-07-10'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-9m9w-gxf7-rh8m'
references:
  - url: >-
      https://github.com/elixir-tesla/tesla/security/advisories/GHSA-9m9w-gxf7-rh8m
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-48595'
  - url: >-
      https://github.com/elixir-tesla/tesla/commit/db963dba67651b9abd1fc420a1d9679cf6efe182
  - url: 'https://cna.erlef.org/cves/CVE-2026-48595.html'
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-48595'
  - url: 'https://github.com/advisories/GHSA-9m9w-gxf7-rh8m'
tags:
  - ghsa
  - erlang
epss: 0.00487
epssPercentile: 0.41046
ingestedAt: '2026-07-10T00:54:12.237Z'
---

## Overview

### Summary

`Tesla.Middleware.FollowRedirects` is meant to strip the `Authorization` header when following a cross-origin redirect, but performs the check with a case-sensitive comparison against the lowercase string `"authorization"`. Because Tesla preserves header keys exactly as supplied by the caller, any application that sets the header with its RFC 7235 canonical casing (`"Authorization"`) bypasses the filter entirely, leaking bearer tokens or other credentials to whatever origin the redirect points at.

### Details

The filter list in `lib/tesla/middleware/follow_redirects.ex` is defined as `@filter_headers ["authorization", "host"]` and the membership check `k not in @filter_headers` compares the raw key string without case normalization. HTTP header names are case-insensitive per RFC 7230, but Tesla stores them verbatim. A header tuple `{"Authorization", "Bearer …"}` does not match `"authorization"`, so it passes through the filter and is forwarded to the redirect destination unchecked. The same defect applies to the `"Host"` entry.

An attacker who can control a `Location:` response seen by the victim client (their own endpoint, a redirect-open service, or a compromised upstream) receives the credential on the cross-origin follow. No special configuration is required beyond the victim using the standard header casing.

### PoC

1. Configure a Tesla client with `Tesla.Middleware.FollowRedirects` and set the `Authorization` header using canonical casing (`{"Authorization", "Bearer <token>"}`).
2. Make a request to an endpoint that returns a `302` redirect to a different origin.
3. Observe that the `Authorization` header with its value is present in the request delivered to the redirect destination.

### Impact

High severity (CVSS v4.0: 8.2). Any application using `tesla` 1.4.0 through 1.18.2 with `Tesla.Middleware.FollowRedirects` and a non-lowercase `Authorization` header is affected. The workaround is to use all-lowercase `"authorization"` as the header key until upgrading to 1.18.3.

### Workarounds

Normalize all header keys to lowercase before passing them to Tesla. Use `"authorization"` instead of `"Authorization"` when setting headers via `Tesla.put_header/3` or `Tesla.Middleware.Headers`.

### Resources

* Introduction commit: https://github.com/elixir-tesla/tesla/commit/2d937d5813d7cda5cd726f41824985fb655c920f
* Patch commit: https://github.com/elixir-tesla/tesla/commit/db963dba67651b9abd1fc420a1d9679cf6efe182

## Affected packages

- `tesla >= 0.6.0, < 1.18.3`

## Remediation

Upgrade to a patched release:

- `tesla 1.18.3`