Summary
Plug.Cowboy vulnerable to unauthenticated remote DoS via HTTP/2 :scheme atom-table exhaustion
An unauthenticated remote denial-of-service vulnerability in Plug.Cowboy.Conn allows any attacker who can reach an HTTPS Plug.Cowboy listener via HTTP/2 to permanently exhaust the BEAM atom table and crash the entire Erlang VM.
Am I Affected?
All users running plug_cowboy with HTTP/2 may be affected, this includes Phoenix applications. If another HTTP adapter such as Bandit is used, then the consuming project is not affected. If the HTTP/2 endpoint is exposed directly (without a proxy) then the project will be affected. If a proxy is in use then it depends on the proxy configuration. Many proxies use HTTP/1.1 internally, and would be unaffected.
Mitigation
Users are advised to update to plug_cowboy v2.8.1 to mitigate this issue.
Credits
Plug.Cowboy thanks Peter Ullrich for finding and responsibly disclosing this vulnerability.
Impact
The vulnerability will allow crashing the Erlang VM (BEAM) via atom exhaustion.
The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-32688? CVE-2026-32688 is a high-severity allocation of resources without limits or throttling vulnerability in plug_cowboy (erlang), affecting versions >= 2.0.0, < 2.8.1. It is fixed in 2.8.1. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
- Which versions of plug_cowboy are affected by CVE-2026-32688? plug_cowboy (erlang) versions >= 2.0.0, < 2.8.1 is affected.
- Is there a fix for CVE-2026-32688? Yes. CVE-2026-32688 is fixed in 2.8.1. Upgrade to this version or later.
- Is CVE-2026-32688 exploitable, and should I be worried? Whether CVE-2026-32688 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-32688 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-32688? Upgrade
plug_cowboyto 2.8.1 or later.