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 before 1.16.6, from 1.17.0 before 1.17.4, from 1.18.0 before 1.18.5, from 1.19.0 before 1.19.5, and from 1.20.0 before 1.20.3.

AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CWE-770

https://cna.erlef.org/cves/CVE-2026-56814.html

https://github.com/elixir-plug/plug/commit/0ee8afcc61466dc5f7a8f048d0632c899165b81f

https://github.com/elixir-plug/plug/commit/56edca2ce35fe5589cd581644d8a4493fa5f484e

https://github.com/elixir-plug/plug/commit/981597d3a4271ede64373c7a731702a42c500dd6

https://github.com/elixir-plug/plug/commit/cae36053350e5215a4e0ca33cd130af9c5fc6364

https://github.com/elixir-plug/plug/commit/df97d3f17f808a9916a7700a701fb85314559d56

https://github.com/elixir-plug/plug/commit/f7effaed811c00b5f5bf817936bfd9c5df27b7dc

https://github.com/elixir-plug/plug/security/advisories/GHSA-95qv-c9g9-rm63

https://osv.dev/vulnerability/EEF-CVE-2026-56814

[{"vendor":"elixir-plug","product":"plug","defaultStatus":"unaffected","collectionURL":"https://repo.hex.pm","packageName":"plug","cpes":["cpe:2.3:a:elixir-plug:plug:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Plug.Parsers.MULTIPART'"],"programFiles":["lib/plug/parsers/multipart.ex"],"programRoutines":[{"name":"'Elixir.Plug.Parsers.MULTIPART':parse_multipart/2"},{"name":"'Elixir.Plug.Parsers.MULTIPART':parse_multipart_headers/5"},{"name":"'Elixir.Plug.Parsers.MULTIPART':parse_multipart_body/4"},{"name":"'Elixir.Plug.Parsers.MULTIPART':parse_multipart_file/4"}],"repo":"https://github.com/elixir-plug/plug","packageURL":"pkg:hex/plug","versions":[{"version":"1.4.0","lessThan":"1.16.6","versionType":"semver","status":"affected"},{"version":"1.17.0","lessThan":"1.17.4","versionType":"semver","status":"affected"},{"version":"1.18.0","lessThan":"1.18.5","versionType":"semver","status":"affected"},{"version":"1.19.0","lessThan":"1.19.5","versionType":"semver","status":"affected"},{"version":"1.20.0","lessThan":"1.20.3","versionType":"semver","status":"affected"}]},{"vendor":"elixir-plug","product":"plug","defaultStatus":"unaffected","collectionURL":"https://github.com","packageName":"elixir-plug/plug","cpes":["cpe:2.3:a:elixir-plug:plug:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Plug.Parsers.MULTIPART'"],"programFiles":["lib/plug/parsers/multipart.ex"],"programRoutines":[{"name":"'Elixir.Plug.Parsers.MULTIPART':parse_multipart/2"},{"name":"'Elixir.Plug.Parsers.MULTIPART':parse_multipart_headers/5"},{"name":"'Elixir.Plug.Parsers.MULTIPART':parse_multipart_body/4"},{"name":"'Elixir.Plug.Parsers.MULTIPART':parse_multipart_file/4"}],"repo":"https://github.com/elixir-plug/plug","packageURL":"pkg:github/elixir-plug/plug","versions":[{"version":"c52b2f32c90bccd718202bafccb5f95594e30183","lessThan":"*","versionType":"git","status":"affected","changes":[{"at":"981597d3a4271ede64373c7a731702a42c500dd6","status":"unaffected"},{"at":"56edca2ce35fe5589cd581644d8a4493fa5f484e","status":"unaffected"},{"at":"0ee8afcc61466dc5f7a8f048d0632c899165b81f","status":"unaffected"},{"at":"cae36053350e5215a4e0ca33cd130af9c5fc6364","status":"unaffected"},{"at":"f7effaed811c00b5f5bf817936bfd9c5df27b7dc","status":"unaffected"},{"at":"df97d3f17f808a9916a7700a701fb85314559d56","status":"unaffected"}]}]}]