elixir-plug up to 1.19.2 lib/plug/conn/query.ex algorithmic complexity

Summaryinfo

A vulnerability, which was classified as problematic, has been found in elixir-plug plug up to 1.15.4/1.16.3/1.17.1/1.18.2/1.19.2. Affected is an unknown function in the library lib/plug/conn/query.ex. This manipulation causes algorithmic complexity. This vulnerability is tracked as CVE-2026-54892. The attack is possible to be carried out remotely. No exploit exists. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in elixir-plug plug up to 1.15.4/1.16.3/1.17.1/1.18.2/1.19.2. It has been declared as problematic. Affected by this vulnerability is an unknown functionality in the library lib/plug/conn/query.ex. The manipulation with an unknown input leads to a algorithmic complexity vulnerability. The CWE definition for the vulnerability is CWE-407. An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached. As an impact it is known to affect availability. The summary by CVE is:

Inefficient algorithmic complexity in Plug's nested-parameter decoder allows an unauthenticated remote attacker to cause denial of service. Plug.Conn.Query.decode/4 (and Plug.Conn.Query.decode_each/2) parse query strings and application/x-www-form-urlencoded request bodies. When a key contains many bracketed segments such as a[a][a][a]=1, the decoder walks the brackets and, for each of the N levels, performs a map operation keyed on an ever-growing binary prefix of the key, hashing the full byte range at each step. The total decode cost is therefore quadratic in the number of nesting levels. With the default Plug.Parsers.URLENCODED body limit of 1,000,000 bytes, a single request can carry roughly 333,000 nesting levels and saturate a BEAM scheduler for minutes. A small number of concurrent requests can saturate all schedulers and render a Plug-based server unresponsive. No authentication or knowledge of application routes is required. This vulnerability is associated with program files lib/plug/conn/query.ex and program routines Plug.Conn.Query.decode/4, Plug.Conn.Query.decode_each/2, Plug.Conn.Query.split_keys/6, Plug.Conn.Query.insert_keys/3, and Plug.Conn.Query.finalize_pointer/2. This issue affects plug from 1.15.0 before 1.15.5, 1.16.4, 1.17.2, 1.18.3, and 1.19.3.

The weakness was disclosed by Braidon Whatley and Jonatan Männchen. The advisory is shared at github.com. This vulnerability is known as CVE-2026-54892 since 06/16/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 1.15.5, 1.16.4, 1.17.2, 1.18.3 or 1.19.3 eliminates this vulnerability.

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Productinfo

Vendor

• elixir-plug

Name

• plug

Version

• 1.15.0
• 1.15.1
• 1.15.2
• 1.15.3
• 1.15.4
• 1.16.0
• 1.16.1
• 1.16.2
• 1.16.3
• 1.17.0
• 1.17.1
• 1.18.0
• 1.18.1
• 1.18.2
• 1.19.0
• 1.19.1
• 1.19.2

Website

• Product: https://github.com/elixir-plug/plug/

CPE 2.3info

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CPE 2.2info

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