Buffer overflow in Espressif Arduino-Esp32
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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.008 (55.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 56th percentile — 55.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.006 · newest: 0.008 · change: +0.003
Affected products
- Espressif Arduino-Esp32 — versions < 3.3.8
Weakness classification (CWE)
References
- github.com/espressif/arduino-esp32/security/advisories/GHSA-8cmm-3887-r32j (Exploit, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-42854?
- CVE-2026-42854 is a critical-severity vulnerability in Espressif Arduino-Esp32, classified under Stack-based Buffer Overflow. CVSS score: 9.8/10. Published 2026-05-12.
- How severe is CVE-2026-42854?
- Critical severity. CVSS v3 base score is 9.8 out of 10.