CVE-2026-23833: Esphome ESPHome Vulnerable To Denial-of-service Vulnerability

MODERATE
Advisory Identifier: GHSA-4h3h-63v6-88qx
Share
CWE-190
Published
Advisory Summary

CVE-2026-23833 is a MODERATE esphome vulnerable to denial-of-service vulnerability (CWE-190: Integer Overflow or Wraparound) affecting Esphome libraries in the PyPI ecosystem. The issue involves esphome vulnerable to denial-of-service via out-of-bounds check bypass in the api component. Remediation is available by upgrading affected packages to version 2025.12.7.

CVE-2026-23833 at a Glance

CVE Identifier CVE-2026-23833
GHSA Identifier GHSA-4h3h-63v6-88qx
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-190: Integer Overflow or Wraparound
Affected Product Esphome
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2026-23833

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

esphome fixed: 2025.12.7 
pip install esphome>=2025.12.7
Verify Direct and Transitive Dependencies

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

pip show esphome

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-23833, inspect your installed packages using pip:

pip show esphome

Analyze the terminal output to locate any version of Esphome in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2025.12.7), your application is affected.

Note: The pip show esphome command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-190: Integer Overflow or Wraparound, where the product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. this occurs when an integer value is incremented to a value that is too large to store in the associated representation. when this occurs, the value may become a very small or negative number. In Esphome, 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 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 - Upgrade to ESPHome 2025.12.7 or later (or 2026.1.0b3 or later) - [Enable API encryption](https://esphome.io/components/api.html#configuration-variables) with a unique key per device - Follow the [Security Best Practices](https://esphome.io/guides/security_best_practices/) ### Severity Low - 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. ### Impact Denial-of-service. An attacker with network access to port 6053 can crash and reboot the device. ### Credits Thanks to [@Mat931](https://github.com/Mat931) for responsibly reporting this vulnerability.

CVE-2026-23833 Affected Esphome Versions

1 component(s)
Fixed Versions:
2025.12.7
Product / Package Ecosystem Affected Versions Fixed Version
esphome
pypi/esphome
PyPI
≥ 2025.9.0
< 2025.12.7
2025.12.7

References

GitHub Advisory / Wiki ADVISORY
https://github.com/esphome/esphome/security/advisories/GHSA-4h3h-63v6-88qx
NVD — CVE-2026-23833 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-23833
Esphome Source Repository REPOSITORY
https://github.com/esphome/esphome/pull/13306
Security Fix Commit FIX COMMIT
https://github.com/esphome/esphome/commit/69d7b6e9210390051318bd8e6410727689de08d6
Esphome Security Information SECURITY
https://esphome.io/guides/security_best_practices
Esphome Source Repository REPOSITORY
https://github.com/esphome/esphome

Frequently Asked Questions

What is CVE-2026-23833?
CVE-2026-23833 is a security vulnerability in Esphome involving ESPHome vulnerable to denial-of-service via out-of-bounds check bypass in the API component under CWE-190: Integer Overflow or Wraparound.
Which Esphome versions are affected?
Affected versions include releases prior to 2025.12.7 across affected packages: esphome.
What version fixes CVE-2026-23833?
Upgrading to 2025.12.7 (or the latest patched release for your respective branch) resolves the vulnerability.
Is esphome affected?
Yes, esphome is affected in releases prior to 2025.12.7. Upgrade your dependency to 2025.12.7 or later.
What CWE is associated with CVE-2026-23833?
CVE-2026-23833 is classified under CWE-190: Integer Overflow or Wraparound (The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.).
How can I check PyPI dependencies for CVE-2026-23833?
Run the dependency tree command: 'pip show esphome'. 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-4h3h-63v6-88qx",
  "modified" : "2026-01-21T01:02:49Z",
  "published" : "2026-01-21T01:02:49Z",
  "aliases" : [ "CVE-2026-23833" ],
  "summary" : "ESPHome vulnerable to denial-of-service via out-of-bounds check bypass in the API component",
  "details" : "### Summary\nAn integer overflow in the API component's protobuf decoder allows denial-of-service attacks when API encryption is not used.\n\n### Details\nThe 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.\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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "esphome"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2025.9.0"
      }, {
        "fixed" : "2025.12.7"
      } ]
    } ]
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-190" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-01-21T01:02:49Z",
    "nvd_published_at" : "2026-01-19T18:16:06Z"
  }
}