GHSA-4H3H-63V6-88QX

Vulnerability from github – Published: 2026-01-21 01:02 – Updated: 2026-01-21 01:02
VLAI?
Summary
ESPHome vulnerable to denial-of-service via out-of-bounds check bypass in the API component
Details

Summary

An integer overflow in the API component's protobuf decoder allows denial-of-service attacks when API encryption is not used.

Details

The bounds check ptr + field_length > end in components/api/proto.cpp can overflow when a malicious client sends a large field_length value. This affects all ESPHome device platforms (ESP32, ESP8266, RP2040, LibreTiny). The overflow bypasses the out-of-bounds check, causing the device to read invalid memory and crash.

When using the plaintext API protocol, this attack can be performed without authentication. When noise encryption is enabled, knowledge of the encryption key is required.

Affected Versions

ESPHome 2025.9.0 through 2025.12.6

Mitigation

Severity

Low - Users following Security Best Practices with API encryption enabled are not affected without knowledge of the encryption key.

Impact

Denial-of-service. An attacker with network access to port 6053 can crash and reboot the device.

Credits

Thanks to @Mat931 for responsibly reporting this vulnerability.

Severity ?
6.8 (Medium)
CVSS:4.0/AV:A/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "esphome"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2025.9.0"
            },
            {
              "fixed": "2025.12.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-23833"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-190"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-01-21T01:02:49Z",
    "nvd_published_at": "2026-01-19T18:16:06Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nAn integer overflow in the API component\u0027s protobuf decoder allows denial-of-service attacks when API encryption is not used.\n\n### Details\nThe bounds check `ptr + field_length \u003e end` in `components/api/proto.cpp` can overflow when a malicious client sends a large `field_length` value. This affects all ESPHome device platforms (ESP32, ESP8266, RP2040, LibreTiny). The overflow bypasses the out-of-bounds check, causing the device to read invalid memory and crash.\n\nWhen using the plaintext API protocol, this attack can be performed without authentication. When noise encryption is enabled, knowledge of the encryption key is required.\n\n### Affected Versions\nESPHome 2025.9.0 through 2025.12.6\n\n### Mitigation\n- Upgrade to ESPHome 2025.12.7 or later (or 2026.1.0b3 or later)\n- [Enable API encryption](https://esphome.io/components/api.html#configuration-variables) with a unique key per device\n- Follow the [Security Best Practices](https://esphome.io/guides/security_best_practices/)\n\n### Severity\nLow - Users following [Security Best Practices](https://esphome.io/guides/security_best_practices/) with API encryption enabled are not affected without knowledge of the encryption key.\n\n### Impact\nDenial-of-service. An attacker with network access to port 6053 can crash and reboot the device.\n\n### Credits\nThanks to [@Mat931](https://github.com/Mat931) for responsibly reporting this vulnerability.",
  "id": "GHSA-4h3h-63v6-88qx",
  "modified": "2026-01-21T01:02:49Z",
  "published": "2026-01-21T01:02:49Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/esphome/esphome/security/advisories/GHSA-4h3h-63v6-88qx"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23833"
    },
    {
      "type": "WEB",
      "url": "https://github.com/esphome/esphome/pull/13306"
    },
    {
      "type": "WEB",
      "url": "https://github.com/esphome/esphome/commit/69d7b6e9210390051318bd8e6410727689de08d6"
    },
    {
      "type": "WEB",
      "url": "https://esphome.io/guides/security_best_practices"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/esphome/esphome"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:A/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "ESPHome vulnerable to denial-of-service via out-of-bounds check bypass in the API component"
}


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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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