CVE-2026-56813: elixir-plug plug

Vulnerability summary

CVE-2026-56813 is a low (CVSS 2.1) vulnerability in elixir-plug plug. EPSS estimates a 0.22% chance of exploitation in the next 30 days, higher than 11.1% of scored vulnerabilities.

Timeline

1. 10-07-2026
   PublishedVulnerability first disclosed.
2. 24-09-2026
   Last modifiedVulnerability information updated.

Description

Improper Neutralization of Parameter/Argument Delimiters vulnerability in elixir-plug plug allows an attacker to inject or override HTTP cookie attributes. The Plug.Conn.Cookies.encode/2 function in lib/plug/conn/cookies.ex builds the Set-Cookie response header by interpolating the cookie value and its path, domain, same_site, and extra attributes directly into the header without neutralizing the ; delimiter that separates cookie attributes. An application that places attacker-controlled data into a cookie value or attribute (for example via Plug.Conn.put_resp_cookie/4 when reflecting a username or preference) lets an attacker inject a ; to append or override cookie attributes (such as Domain and Path scope, or dropping the Secure and HttpOnly flags), enabling cookie tossing and session fixation. Carriage return, line feed, and null bytes are rejected by Plug.Conn header validation, so HTTP response splitting is not possible, but attribute injection through ; is not prevented. This issue affects plug: from 0.1.0 before 1.16.6, from 1.17.0 before 1.17.4, from 1.18.0 before 1.18.5, from 1.19.1 before 1.19.5, and from 1.20.0 before 1.20.3.

• CWE-141Improper Neutralization of Parameter/Argument DelimitersThe product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as parameter or argument delimiters when they are sent to a downstream component.