CVE-2026-56814
Plug: multipart :length limit is not charged for part headers, enabling unbounded temp-file creation (denial of service)
Vulnerability description
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.
Affected
pkg:hex/plug
| Status | Type | Version | Changes / Fixed in |
|---|---|---|---|
| affected | semver ⓘ | 1.4.0
|
< 1.16.6
|
| affected | semver ⓘ | 1.17.0
|
< 1.17.4
|
| affected | semver ⓘ | 1.18.0
|
< 1.18.5
|
| affected | semver ⓘ | 1.19.0
|
< 1.19.5
|
| affected | semver ⓘ | 1.20.0
|
< 1.20.3
|
pkg:github/elixir-plug/plug
| Module | Source File | Routine |
|---|---|---|
Plug.Parsers.MULTIPART
|
lib/plug/parsers/multipart.ex
|
Plug.Parsers.MULTIPART.parse_multipart/2
|
Plug.Parsers.MULTIPART.parse_multipart_headers/5
|
||
Plug.Parsers.MULTIPART.parse_multipart_body/4
|
||
Plug.Parsers.MULTIPART.parse_multipart_file/4
|
| Status | Type | Version | Changes / Fixed in |
|---|---|---|---|
| affected | git ⓘ | c52b2f32c9
|
|
References
- https://github.com/elixir-plug/plug/security/advisories/GHSA-95qv-c9g9-rm63 vendor-advisory related
- https://osv.dev/vulnerability/EEF-CVE-2026-56814 related
- https://github.com/elixir-plug/plug/commit/981597d3a4271ede64373c7a731702a42c500dd6 patch
- https://github.com/elixir-plug/plug/commit/56edca2ce35fe5589cd581644d8a4493fa5f484e patch
- https://github.com/elixir-plug/plug/commit/0ee8afcc61466dc5f7a8f048d0632c899165b81f patch
- https://github.com/elixir-plug/plug/commit/cae36053350e5215a4e0ca33cd130af9c5fc6364 patch
- https://github.com/elixir-plug/plug/commit/f7effaed811c00b5f5bf817936bfd9c5df27b7dc patch
- https://github.com/elixir-plug/plug/commit/df97d3f17f808a9916a7700a701fb85314559d56 patch
Credits
- Finder: Peter Ullrich
- Analyst: Jonatan Männchen
- Remediation developer: José Valim
CVE record as JSON:
GET /cves/CVE-2026-56814.json
OSV record as JSON:
GET /osv/EEF-CVE-2026-56814.json