CVE-2026-42854

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 v3.1 Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0028

Probability of exploitation

0.52%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-121 CWE-121

Affected Products

Vendor	Product	Versions
espressif	arduino-esp32	< 3.3.8

References

Advisories & Patches

https://github.com/espressif/arduino-esp32/security/advisories/GHSA-8cmm-3887-r32j https://github.com/espressif/arduino-esp32/security/advisories/GHSA-8cmm-3887-r32j

Exploits

https://github.com/espressif/arduino-esp32/security/advisories/GHSA-8cmm-3887-r32j https://github.com/espressif/arduino-esp32/security/advisories/GHSA-8cmm-3887-r32j

Frequently Asked Questions

What is CVE-2026-42854? +

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. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-42854? +

CVE-2026-42854 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0028, placing it in the 1th percentile for exploitation probability.

What products are affected by CVE-2026-42854? +

CVE-2026-42854 affects products from espressif, specifically: arduino-esp32. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-42854? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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