CVE-2026-42854

CriticalPublic PoC

Published: 12 May 2026

Published

12 May 2026

Modified

18 May 2026

KEV Added

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Patch

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CVSS Score v3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0057 43.0th percentile

Risk Priority 70 floored blend · peak EPSS

Summary

CVE-2026-42854 is a critical-severity Stack-based Buffer Overflow (CWE-121) vulnerability in Espressif Arduino-Esp32. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 43.0th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

EU & UK References

🇪🇺 ENISA EUVD: EUVD-2026-29858

Vulnerability details

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.

CWE(s): CWE-121

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

Why these techniques?

Stack buffer overflow in WebServer multipart parser allows remote exploitation via crafted HTTP Content-Type header, directly enabling T1190 on a public-facing web service.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0