Riskcovery

CVE-2026-32688

Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy

State
Published
Severity
8.7 High
Published
Apr 27, 2026
Updated
Apr 29, 2026
Reserved
Mar 13, 2026

Read the record on cve.org

Description

Allocation of Resources Without Limits or Throttling vulnerability in elixir-plug plug_cowboy allows unauthenticated remote denial of service via atom table exhaustion.

Plug.Cowboy.Conn.conn/1 in lib/plug/cowboy/conn.ex calls String.to_atom/1 on the value returned by :cowboy_req.scheme/1. For HTTP/2 connections, cowlib passes the client-supplied :scheme pseudo-header value through verbatim without validation. Each unique value permanently allocates a new entry in the BEAM atom table. Since atoms are never garbage-collected and the atom table has a fixed limit (default 1,048,576), an unauthenticated attacker can exhaust the table by sending HTTP/2 requests with unique :scheme values, causing the Erlang VM to abort with system_limit and taking down the entire node.

This vulnerability does not affect HTTP/1.1, where cowboy derives the scheme from the listener type rather than from a client-supplied header.

This issue affects plug_cowboy: from 2.0.0 before 2.8.1.

Scores

CVSSScoreVectorSource
4.08.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:NEEF

Weaknesses

  • CWE-770 Allocation of Resources Without Limits or Throttling

Affected Products

ProductVersions
plug_cowboyelixir-plug
  • 2.0.0 to before 2.8.1Affected
plug_cowboyelixir-plug
  • 12ecfd024bb179d48b018fecf074e43fe6a19c83 to before bfb34cb45eb354e56437f7023fb306de1bf9c19bAffected

References

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