CVE-2026-42854Public exploitNetwork attack vector

Remote crash via oversized multipart boundary

Published May 12, 2026 · Updated May 12, 2026

Stack buffer overflow in Espressif Arduino-ESP32 before 3.3.8 allows remote attackers to crash an ESP32 device over Wi-Fi. The WebServer multipart parser allocates a stack VLA sized from the Content-Type boundary without first enforcing a length limit. A device must run Arduino WebServer with a file upload handler; one unauthenticated request reliably reboots it, while code execution depends on memory layout.

CVSS severity9.8
Critical
EPSS probability0.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack buffer overflow in Espressif Arduino-ESP32 before 3.3.8 allows remote attackers to crash an ESP32 device over Wi-Fi. The WebServer multipart parser allocates a stack VLA sized from the Content-Type boundary without first enforcing a length limit. A device must run Arduino WebServer with a file upload handler; one unauthenticated request reliably reboots it, while code execution depends on memory layout.

The record

CVE
CVE-2026-42854
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Espressif Systems
Product
Arduino-ESP32
Classifications
CWE-121, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.3.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Espressif Systems · Arduino-ESP32version=< 3.3.8

Published CVSS scores

9.8GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-121Stack-based Buffer Overflow
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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