CVE-2026-32688 — plug_cowboy
Fix: elixir-plug/plug_cowboy@bfb34cbCVE-2026-32688 is a security vulnerability in plug_cowboy. A fix is available for plug_cowboy — see the affected versions and patch details below.
Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-32688.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
plug_cowboyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Hex packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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.
Impact
The vulnerability will allow crashing the Erlang VM (BEAM) via atom exhaustion.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💧Hex | plug_cowboy | ≥ 2.0.0&&< 2.8.1 | 2.8.1mix deps.update plug_cowboy |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for plug_cowboy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update plug_cowboy to 2.8.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-32688 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-32688 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-32688. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-32688 in your dependencies?
O3 Security finds CVE-2026-32688 across Hex dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.