CVE-2026-32688: Plug cowboy Scheme` Atom-table Exhaustion Vulnerability

HIGH
Advisory Identifier: GHSA-q8x4-x7mp-5vg2
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CWE-770
Published
Advisory Summary

CVE-2026-32688 is a HIGH scheme` atom-table exhaustion vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting Plug cowboy libraries in the Hex ecosystem. The issue involves scheme` atom-table exhaustion. Remediation is available by upgrading affected packages to version 2.8.1.

CVE-2026-32688 at a Glance

CVE Identifier CVE-2026-32688
GHSA Identifier GHSA-q8x4-x7mp-5vg2
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product Plug cowboy
Package Ecosystem Hex
Published Date
Last Updated

How to Fix CVE-2026-32688

To remediate this vulnerability, upgrade all affected Plug cowboy dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

plug_cowboy fixed: 2.8.1 
Upgrade plug_cowboy to 2.8.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for plug_cowboy

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-32688, inspect your project dependencies for Plug cowboy:

inspect dependencies for plug_cowboy

Analyze the terminal output to locate any version of Plug cowboy in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.8.1), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. In Plug cowboy, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## 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.

CVE-2026-32688 Affected Plug cowboy Versions

1 component(s)
Fixed Versions:
2.8.1
Product / Package Ecosystem Affected Versions Fixed Version
plug_cowboy
 Hex
≥ 2.0.0
< 2.8.1
2.8.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2
NVD — CVE-2026-32688 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-32688
Security Fix Commit FIX COMMIT
https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b
cna.erlef.org/cves/cve-2026-32688... WEB
https://cna.erlef.org/cves/CVE-2026-32688.html
Plug cowboy Source Repository REPOSITORY
https://github.com/elixir-plug/plug_cowboy
osv.dev/vulnerability/eef-c... WEB
https://osv.dev/vulnerability/EEF-CVE-2026-32688

Frequently Asked Questions

What is CVE-2026-32688?
CVE-2026-32688 is a security vulnerability in Plug cowboy involving scheme` atom-table exhaustion under CWE-770: Allocation of Resources Without Limits or Throttling.
Which Plug cowboy versions are affected?
Affected versions include releases prior to 2.8.1 across affected packages: plug_cowboy.
What version fixes CVE-2026-32688?
Upgrading to 2.8.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is plug_cowboy affected?
Yes, plug_cowboy is affected in releases prior to 2.8.1. Upgrade your dependency to 2.8.1 or later.
What CWE is associated with CVE-2026-32688?
CVE-2026-32688 is classified under CWE-770: Allocation of Resources Without Limits or Throttling (The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.).
How can I check Hex dependencies for CVE-2026-32688?
Run the dependency tree command: 'inspect dependencies for plug_cowboy'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q8x4-x7mp-5vg2",
  "modified" : "2026-05-05T21:46:09Z",
  "published" : "2026-05-05T21:46:09Z",
  "aliases" : [ "CVE-2026-32688" ],
  "summary" : "Plug.Cowboy vulnerable to unauthenticated remote DoS via HTTP/2 `:scheme` atom-table exhaustion",
  "details" : "## Summary\n\nAn 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.\n\n## Am I Affected?\n\nAll 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.\n\n## Impact\n\nThe vulnerability will allow crashing the Erlang VM (BEAM) via atom exhaustion.\n\n## Mitigation\n\nUsers are advised to update to plug_cowboy v2.8.1 to mitigate this issue.\n\n## Credits\nPlug.Cowboy thanks Peter Ullrich for finding and responsibly disclosing this vulnerability.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Hex",
      "name" : "plug_cowboy"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.0.0"
      }, {
        "fixed" : "2.8.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-32688"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b"
  }, {
    "type" : "WEB",
    "url" : "https://cna.erlef.org/cves/CVE-2026-32688.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/elixir-plug/plug_cowboy"
  }, {
    "type" : "WEB",
    "url" : "https://osv.dev/vulnerability/EEF-CVE-2026-32688"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-05T21:46:09Z",
    "nvd_published_at" : "2026-04-27T14:16:47Z"
  }
}