EEF-CVE-2026-48595 CVE-2026-48595 GHSA-9m9w-gxf7-rh8m

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

Medium Hex

Severity: 0.0 / 10; Medium · CVSS 4.0
Exploit chance (EPSS): 0.49%; Chance of exploitation in the next 30 days. Higher than 41.94% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-178 Improper Handling of Case Sensitivity
Fix: 1.18.3; Upgrade tesla to this version or later

Description

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.

Affected versions

Hex

Package	Vulnerable	Fixed in
tesla	`>= 1.4.0, < 1.18.3`	`1.18.3`
tesla	`>= 0.6.0, < 1.18.3`	`1.18.3`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

tesla Hex → `1.18.3`

mix

{:tesla, "~> 1.18.3"} # then: mix deps.update tesla

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: Low
Attack requirements: Present
Privileges required: None
User interaction: None
Confidentiality (vulnerable system): High
Integrity (vulnerable system): None
Availability (vulnerable system): None
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

CVSS 3.1 5.9

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Attack vector: Network
Attack complexity: High
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Weakness

CWE-178: Improper Handling of Case Sensitivity

The product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results.

How to prevent it

Architecture and Design: Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.
Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

References

Advisories

Fixes and patches

github.com/elixir-tesla/tesla/commit/db963dba67651b9abd1fc420a1d9679cf6efe182

Packages

Timeline

Jun 2, 2026 Published
Sep 24, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
EEF-CVE-2026-48596 CRLF injection in Tesla.Multipart.add_content_type_param/2 allows HTTP header injection	Low	Also affects tesla
EEF-CVE-2026-48594 Decompression bomb in Tesla.Middleware.DecompressResponse and Tesla.Middleware.Compression	High	Also affects tesla
EEF-CVE-2026-48597 Atom table exhaustion via untrusted URL scheme in Tesla.Adapter.Mint	Medium	Also affects tesla
GHSA-28jh-g32x-v9v4 CRLF injection in Tesla.Multipart disposition parameters allows multipart part header injection	Low	Also affects tesla
GHSA-vjh5-4x84-xrqp Nuxt: Server-side route rules (`redirect`, `headers`, `proxy`, `ssr`) are skipped for case-variant paths when routing is case-insensitive	Medium	Same weakness, CWE-178
GHSA-f72v-6w45-q472 undici vulnerable to Subresource Integrity bypass via non-lowercase algorithm tokens	High	Same weakness, CWE-178
GHSA-389g-gv7q-r4x8 fastify is vulnerable to header validation bypass via case-sensitive propertyNames	Low	Same weakness, CWE-178
GHSA-hmp2-4m7g-22cv Backstage: Scaffolder action input authorization bypass	High	Same weakness, CWE-178

Credits: Jonatan Männchen / EEF, Peter Ullrich, Yordis Prieto

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