Executive brief
Tesla is a popular HTTP client library for the Elixir programming language. A vulnerability exists where the library fails to properly check for line breaks in certain request headers, which could allow an attacker to inject unauthorized headers into outbound web requests. This could lead to request smuggling or the forging of request metadata, potentially bypassing security controls on the receiving server.
Technical details
A CRLF injection vulnerability exists in Tesla.Multipart.add_content_type_param/2 within lib/tesla/multipart.ex. The function appends caller-supplied strings to the multipart Content-Type header without validating or neutralizing carriage return (\r) and line feed (\n) characters. An attacker who can control content-type parameters (such as charset or boundary values) can inject arbitrary HTTP headers into outbound requests. This can lead to HTTP request splitting or smuggling against upstream servers. The issue is fixed in version 1.18.3 by implementing proper validation of parameter strings.
Affected products
- elixir-tesla Tesla >= 0.8.0, < 1.18.3
Timeline
- 2026-06-02: disclosed: Initial disclosure and NVD publication
- 2026-07-10: advisory: GitHub Advisory published
- 1.18.3: patched