CVE-2026-32688 Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy
Unauthenticated attackers can crash the Erlang VM by exhausting the atom table via malicious HTTP/2 scheme headers in plug_cowboy.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-32688?
CVE-2026-32688 is a high-severity denial of service vulnerability in elixir-plug plug_cowboy, published on 27 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-770
Which versions are affected by CVE-2026-32688?
3 open source packages ship an affected version, including plug_cowboy. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
plug_cowboy Hex | From 2.0.0 | 2.8.1 |
plug_cowboy Hex | From 2.0.0 | 2.8.1 |
plug_cowboy Hex | From 2.0.0 | 2.8.1 |
Products include Elixir-Plug Plug.cowboy.
How do I fix CVE-2026-32688?
Upgrade plug_cowboy to 2.8.1 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-32688 being exploited?
There is no known exploitation of CVE-2026-32688 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-32688, GHSA-q8x4-x7mp-5vg2.