Authorization header leaks to third-party origin on cross-origin redirect in Tesla.Middleware.FollowRedirects

Summary

Improper Handling of Case Sensitivity vulnerability in elixir-tesla tesla allows credential leakage to a third-party origin on cross-origin redirects. Tesla.Middleware.FollowRedirects strips security-sensitive headers on cross-origin redirects using a case-sensitive string comparison against a lowercase filter list (@filter_headers ["authorization", "host"]). HTTP header names are case-insensitive per RFC 7230, but Tesla preserves header keys verbatim as supplied by the caller without normalizing case. A header set as {"Authorization", "Bearer …"} (the RFC 7235 canonical casing used by virtually all HTTP libraries and documentation) does not match the lowercase filter entry and is forwarded to the redirect destination. An attacker who can control or influence a Location: response seen by the client (via their own endpoint, a redirect-open upstream, or a compromised origin) receives the bearer token or other Authorization material on the cross-origin request. This issue affects tesla: from 1.4.0 before 1.18.3.

Timeline

1. Jun 2, 2026, 7:08 PM UTCCVE published
2. Jun 3, 2026, 3:59 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. Sep 24, 2026, 8:51 PM UTCRecord last updated

Affected versions

• tesla

  From 1.4.0 · fixed in 1.18.3

• elixir-tesla/tesla

  From 2d937d5813d7cda5cd726f41824985fb655c920f · fixed in db963dba67651b9abd1fc420a1d9679cf6efe182

• teslaHex

  From 1.4.0 · fixed in 1.18.3

• teslaHex

  From 0.6.0 · fixed in 1.18.3

References 5