Vulnerability · Published Apr 27, 2026 · Assigned by EEF

CVE-2026-32688Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy

High 8.7

In plain English

A high-severity resource allocation without limits in plug_cowboy from elixir-plug. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 46% of all known vulnerabilities).

Severity (CVSS 4.0)8.7High

Exploit odds (30 days)0.5%top 54.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected products (as reported)

Vendor	Product	Versions
elixir-plug	plug_cowboy	2.0.0 – before 2.8.1
elixir-plug	plug_cowboy	12ecfd024bb179d48b018fecf074e43fe6a19c83 – before bfb34cb45eb354e56437f7023fb306de1bf9c19b

Weakness: CWE-770 · Vector: 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

References

https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2 vendor-advisory, related
https://cna.erlef.org/cves/CVE-2026-32688.html related
https://osv.dev/vulnerability/EEF-CVE-2026-32688 related
https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b patch