How severe is CVE-2026-42855?

CVE-2026-42855 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2026-42855 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (41st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-42855?

CVE-2026-42855 affects Espressif Arduino-esp32. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-42855?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-42855 have an EU (EUVD) identifier?

Yes. CVE-2026-42855 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29859.

When was CVE-2026-42855 published?

CVE-2026-42855 was published on 2026-05-12 and last updated on 2026-06-17.

CVE-2026-42855

CVE-2026-42855 is a high-severity vulnerability in Espressif Arduino-esp32 with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-287.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 1% (41st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-29859
Weakness: CWE-287
Affected product: Espressif Arduino-esp32
Published: 2026-05-12
Last modified: 2026-06-17

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 Digest authentication implementation in arduino-esp32 computes the authentication hash using the URI field from the client's Authorization header, without verifying that it matches the actual requested URI. This allows an attacker who possesses any valid digest response (computed for URI-A) to authenticate requests to a completely different protected URI (URI-B), bypassing per-resource access control. This vulnerability is fixed in 3.3.8.

Frequently asked questions

What is CVE-2026-42855?: 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 Digest authentication implementation in arduino-esp32 computes the authentication hash using the URI field from the client's Authorization header, without verifying that it matches the actual requested URI. This allows an attacker who possesses any valid digest response (computed for URI-A) to authenticate requests to a completely different protected URI (URI-B), bypassing per-resource access control. This vulnerability is fixed in 3.3.8.
How severe is CVE-2026-42855?: CVE-2026-42855 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2026-42855 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (41st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-42855?: CVE-2026-42855 affects Espressif Arduino-esp32. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-42855?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-42855 have an EU (EUVD) identifier?: Yes. CVE-2026-42855 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29859.
When was CVE-2026-42855 published?: CVE-2026-42855 was published on 2026-05-12 and last updated on 2026-06-17.

References

https://github.com/espressif/arduino-esp32/security/advisories/GHSA-28hv-fwm3-rpcq

Affected products (1)

cpe:2.3:a:espressif:arduino-esp32:*:-:*:*:*:*:*:*

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