Executive brief
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.
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