CVE-2026-42855: Espressif arduino-esp32 authentication bypass in WebServer Digest auth

CVE-2026-42855 · Severity: high · CVSS 7.5 · Published 2026-05-12

A security flaw exists in the software core used by many ESP32-based smart devices and microcontrollers. The vulnerability affects the 'Digest' authentication method, which is used to protect web-based control panels and APIs with a password. An attacker can bypass these security checks to access restricted administrative pages by reusing valid credentials intended for a different, less sensitive part of the device.

Vendors: Espressif Systems.

Quick answers

Is CVE-2026-42855 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-42855 being exploited in the wild.
How severe is CVE-2026-42855?
High severity, with a CVSS score of 7.5, published 12 May 2026.
Which products and versions are affected?
Espressif Systems Arduino-Esp32 <= 3.3.7.
Is there a fix for CVE-2026-42855?
A patch was published on 2026-04-12: Fix released in version 3.3.8 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-42855 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-42855?
Check whether you run Espressif Systems Arduino-Esp32 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is an improper authentication flaw (CWE-287) within the WebServer component of the arduino-esp32 core. The root cause is that the server computes the HA2 hash using the 'uri' field provided in the client-supplied Authorization header without validating it against the actual request URI. Consequently, a valid digest response generated for one resource (URI-A) can be successfully replayed to authenticate a request for a different protected resource (URI-B). This allows an attacker to escalate privileges or access administrative endpoints if they possess valid credentials for any single endpoint on the device. The issue is fixed in version 3.3.8 by adding a comparison between the header URI and the actual request URI.

Affected products

  • Espressif Systems arduino-esp32 <= 3.3.7

Timeline

  • 2026-03-27: disclosed: Vulnerability reported to Espressif
  • 2026-04-12: patched: Fix released in version 3.3.8
  • 2026-05-12: advisory: CVE-2026-42855 published

References

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