{"id":"CVE-2026-48595","aliases":["EEF-CVE-2026-48595","GHSA-9m9w-gxf7-rh8m"],"url":"https://o3.security/vulnerability/CVE-2026-48595","summary":"Authorization header leaks to third-party origin on cross-origin redirect in Tesla.Middleware.FollowRedirects","details":"### Summary\n\n`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.\n\n### Details\n\nThe 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.\n\nAn 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.\n\n### PoC\n\n1. Configure a Tesla client with `Tesla.Middleware.FollowRedirects` and set the `Authorization` header using canonical casing (`{\"Authorization\", \"Bearer <token>\"}`).\n2. Make a request to an endpoint that returns a `302` redirect to a different origin.\n3. Observe that the `Authorization` header with its value is present in the request delivered to the redirect destination.\n\n### Impact\n\nHigh 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.\n\n### Workarounds\n\nNormalize 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`.\n\n### Resources\n\n* Introduction commit: https://github.com/elixir-tesla/tesla/commit/2d937d5813d7cda5cd726f41824985fb655c920f\n* Patch commit: https://github.com/elixir-tesla/tesla/commit/db963dba67651b9abd1fc420a1d9679cf6efe182","published":"2026-06-02T19:08:48.339Z","modified":"2026-09-26T03:45:53.473009710Z","cvss":null,"epss":{"score":0.00487,"percentile":0.40836,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Hex","name":"tesla","fixedVersion":"1.18.3"}],"fix":{"url":"https://github.com/elixir-tesla/tesla/commit/2d937d5813d7cda5cd726f41824985fb655c920f","label":"elixir-tesla/tesla@2d937d5"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-48595.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-48595"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48595.json"},{"type":"ADVISORY","url":"https://github.com/elixir-tesla/tesla/security/advisories/GHSA-9m9w-gxf7-rh8m"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-48595"},{"type":"FIX","url":"https://github.com/elixir-tesla/tesla/commit/2d937d5813d7cda5cd726f41824985fb655c920f"},{"type":"FIX","url":"https://github.com/elixir-tesla/tesla/commit/db963dba67651b9abd1fc420a1d9679cf6efe182"},{"type":"PACKAGE","url":"https://github.com/elixir-tesla/tesla"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-26T03:45:53.473009710Z"}}