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CVE-2026-42854

Espressif Arduino-esp32 remote code execution

9.8 CRITICALPublic exploitEPSS 0.83%
  1. Published12 May 2026

Description

arduino-esp32 is an Arduino core for the ESP32, ESP32-S2, ESP32-S3, ESP32-C3, ESP32-C6 and ESP32-H2 microcontrollers. Prior to 3.3.8, the WebServer multipart form parser in arduino-esp32 allocates a Variable Length Array (VLA) on the stack whose size is derived from an attacker-controlled HTTP header field (Content-Type: multipart/form-data; boundary=...) without enforcing any length limit. Sending a boundary string longer than ~8000 characters overflows the 8192-byte task stack of the loopTask, causing a crash and potential remote code execution. This vulnerability is fixed in 3.3.8.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Espressif Arduino-esp32< 3.3.8

Remediation

Fixed in
Espressif Arduino-esp32≥ 3.3.8

References

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Frequently asked

Is CVE-2026-42854 being actively exploited?

CVE-2026-42854 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.83%.

How severe is CVE-2026-42854?

CVE-2026-42854 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.83% probability of exploitation.

Which products are affected by CVE-2026-42854?

Affected products include Espressif Arduino-esp32.

How do I fix CVE-2026-42854?

Upgrade affected software to a fixed version, for example Espressif Arduino-esp32 3.3.8 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-42854 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.