Plug: quadratic-time decoding of nested query/body parameters enables denial of service

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Summary

CVECVE-2026-54892
StatePUBLISHED
AssignerEEF
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-23 13:16:43 UTC
Updated2026-06-23 15:44:39 UTC
DescriptionInefficient 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.

Risk And Classification

Primary CVSS: v4.0 8.7 HIGH from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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

Problem Types: CWE-407 | CWE-407 CWE-407 Inefficient Algorithmic Complexity

VersionSourceTypeScoreSeverityVector
4.06b3ad84c-e1a6-4bf7-a703-f496b71e49dbSecondary8.7HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/C...
4.0CNACVSS8.7HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
None
Availability
High
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Elixir-plug Plug affected 1.15.0 1.15.5 semver Not specified
CNA Elixir-plug Plug affected 1.16.0 1.16.4 semver Not specified
CNA Elixir-plug Plug affected 1.17.0 1.17.2 semver Not specified
CNA Elixir-plug Plug affected 1.18.0 1.18.3 semver Not specified
CNA Elixir-plug Plug affected 1.19.0 1.19.3 semver Not specified
CNA Elixir-plug Plug affected 712b875d3442c765d8d37e546ffd5ad9f8afcc55 * git Not specified

References

ReferenceSourceLinkTags
github.com/elixir-plug/plug/commit/d4e5568392a4b29e545b91e12e87d6098f976145 6b3ad84c-e1a6-4bf7-a703-f496b71e49db github.com
osv.dev/vulnerability/EEF-CVE-2026-54892 6b3ad84c-e1a6-4bf7-a703-f496b71e49db osv.dev
github.com/elixir-plug/plug/security/advisories/GHSA-j43x-5hjq-rgxf 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/elixir-plug/plug/commit/d737eb236f17e31a36290e39f9ef3cd86a1343bd 6b3ad84c-e1a6-4bf7-a703-f496b71e49db github.com
github.com/elixir-plug/plug/commit/9c5d37c440eaae92869eed7c014c47266744fadb 6b3ad84c-e1a6-4bf7-a703-f496b71e49db github.com
cna.erlef.org/cves/CVE-2026-54892.html 6b3ad84c-e1a6-4bf7-a703-f496b71e49db cna.erlef.org
github.com/elixir-plug/plug/commit/c317d08fdcf96e17931f7419275b2b8c4bf3e951 6b3ad84c-e1a6-4bf7-a703-f496b71e49db github.com
github.com/elixir-plug/plug/commit/a61124aa625d819a218fb07f90afbac8aa85eb0e 6b3ad84c-e1a6-4bf7-a703-f496b71e49db github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Braidon Whatley (en)

CNA: José Valim (en)

CNA: Jonatan Männchen / EEF (en)

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