What’s Vulnerable › Vulnerabilities

CVE-2026-42854: arduino-esp32: Stack buffer overflow in WebServer multipart boundary parsing leads to remote crash potential RCE

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-05-12 · updated 2026-10-26
• Weakness: CWE-121

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.

Affected products

• espressif arduino-esp32: before 3.3.8 — fixed in 3.3.8

How to fix

Upgrade to a fixed version: espressif arduino-esp32 3.3.8. Check the vendor advisory for mitigations.

References

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

Get alerted when CVE-2026-42854 or the next vulnerability affects your stack