CVE-2026-48595

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.

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.

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

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.

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.

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.

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.

Configurations

The application must include Tesla.Middleware.FollowRedirects in its Tesla middleware pipeline.

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