CVE-2026-42854: arduino-esp32 is an Arduino core for the ESP32, ESP32-S2, ESP32-S3, ESP32-C3, ESP32-C6 and ESP32-H2 microcontr

Q: How do I fix CVE-2026-42854?

arduino-esp32: upgrade to 3.3.8. Exact commands for each OS are on this page.

Q: Is CVE-2026-42854 being exploited?

CVE-2026-42854 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-42854 affect?

CVE-2026-42854 affects arduino-esp32. Severity is critical (CVSS 9.8). 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

Q: How urgent is CVE-2026-42854?

Priority 59/100. Critical severity; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2026-42854 is a critical-severity flaw (CVSS 9.8) affecting arduino-esp32. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 o

Why this priority

Critical severity
Public exploit reference
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 53%)
CISA exploited list	No
Weakness	CWE-121
Published	2026-05-12
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: espressif

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-12 22:16 UTCPublished CVE record published
2026-10-26 14:10 UTCUpdated Record last modified

espressif arduino-esp32 UPGRADE

Affected: < 3.3.8

Fixed in: 3.3.8

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy arduino-esp32 || rpm -q arduino-esp32 || arduino-esp32 --version

2. UPGRADE to 3.3.8 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade arduino-esp32

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade arduino-esp32

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Exact fixes by distribution

Fedora ELN · edk2 · FIXED · 20260812-12.eln159 · FEDORA-2026-e316b6370a · source

sudo dnf upgrade --advisory=FEDORA-2026-e316b6370a

Fedora 46 · perl-Mojo-DOM58 · FIXED · 3.003-1.fc46 · FEDORA-2026-d5412af3de · source

sudo dnf upgrade --advisory=FEDORA-2026-d5412af3de

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

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

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-42854?

arduino-esp32: upgrade to 3.3.8. Exact commands for each OS are on this page.

Is CVE-2026-42854 being exploited?

CVE-2026-42854 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-42854 affect?

CVE-2026-42854 affects arduino-esp32. Severity is critical (CVSS 9.8). 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

How urgent is CVE-2026-42854?

Priority 59/100. Critical severity; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-42855 HIGH 7.5 UPGRADE arduino-esp32 is an Arduino core for the ESP32, ESP32-S2, ESP32-S3, ESP32-C3, ESP32-C6 and ESP32-H2 microcontr

References

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