CVE-2026-56814
MediumCVSS 6.9Summary
The multipart parser in the Plug library does not count part headers against the :length budget, allowing an attacker to send a request with many empty-body file parts. Each part with a non-empty filename creates a temporary file, leading to inode, disk, and memory exhaustion. This enables an unauthenticated DoS attack.
Risk Assessment
The organization is vulnerable to a Denial of Service (DoS) attack that exhausts system resources (inodes, disk, memory) via a single HTTP request. No authentication is required; only reachability of a multipart endpoint over HTTP is needed.
Recommendation
Immediately update the Plug library to version 1.16.6, 1.17.4, 1.18.5, 1.19.5, or 1.20.3 (depending on the branch used). If an update is not possible, consider restricting access to multipart endpoints or implementing an additional limit on the number of parts.
Other vulnerabilities in Plug
See all- CVE-2026-56813Low
A vulnerability in the Elixir Plug library, specifically in the Plug.Conn.Cookies.encode/2 function, fails to neutralize the ';' delimiter in cookie attributes. This allows an attacker to inject additional attributes into the Set-Cookie header, potentially overriding existing cookie attributes.
- CVE-2026-54892High
Plug has an efficiency issue in the nested-parameter decoder that allows an unauthenticated remote attacker to cause denial of service. The decoding algorithm's complexity is quadratic in relation to the number of nesting levels, which can lead to server unresponsiveness.
Original NVD description (English source)
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.