CVE-2026-56814: Elixir-Plug Plug

Medium severity, CVSS 6.9. EPSS: 1.1% chance of exploitation in the next 30 days.

Plug.Parsers.MULTIPART, the multipart request-body parser used to handle file uploads and multipart forms, does not enforce its :length budget against all consumed resources, allowing an unauthenticated remote attacker to cause denial of service. The parser charges the :length limit only for part body bytes; part header bytes are never counted, and a part with an empty body costs zero. Because every part whose Content-Disposition carries a non-empty filename creates a fresh temporary file (via Plug.Upload) and retains a Plug.Upload struct for the duration of the request, an attacker can send a single request composed of many empty-body file parts. Such a request stays well under the configured :length limit (8,000,000 bytes by default) while creating one temporary file per part, leading to inode and disk exhaustion and unbounded memory growth. Any application using Plug.Parsers with the :multipart parser is affected, and no authentication is required, only reachability of a multipart endpoint over HTTP. This vulnerability is associated with program files lib/plug/parsers/multipart.ex and program routines Plug.Parsers.MULTIPART.parse_multipart/2, Plug.Parsers.MULTIPART.parse_multipart_headers/5, Plug.Parsers.MULTIPART.parse_multipart_body/4, and Plug.Parsers.MULTIPART.parse_multipart_file/4. This issue affects plug: from 1.4.0-rc.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.

Affected products

• Elixir-Plug Plug: from 1.4.0-rc.0, before 1.16.6 (fixed in 1.16.6); from 1.17.0, before 1.17.4 (fixed in 1.17.4); from 1.18.0, before 1.18.5 (fixed in 1.18.5); from 1.19.1, before 1.19.5 (fixed in 1.19.5); from 1.20.0, before 1.20.3 (fixed in 1.20.3)

Published 2026-07-10. Last modified 2026-09-24.