CVE-2026-42855 espressif CVE debrief

Who should care

Defenders responsible for arduino-esp32 installations, security teams, and developers using the arduino-esp32 core should be aware of this vulnerability and take necessary actions to mitigate it.

Why it matters

The arduino-esp32 core has a vulnerability in its WebServer Digest authentication implementation, allowing an attacker to bypass access control and authenticate requests to protected URIs. Defenders should prioritize verifying exposure and upgrading to version 3.3.8 or later.

• An attacker can bypass access control and authenticate requests to protected URIs without possessing the correct credentials for those URIs.
• Defenders need to verify exposure of arduino-esp32 installations and upgrade to version 3.3.8 or later to prevent exploitation.
• The vulnerability allows for unauthorized access to protected resources, potentially leading to further exploitation.

Technical summary

The arduino-esp32 core for ESP32 microcontrollers has a vulnerability in its WebServer Digest authentication implementation prior to version 3.3.8. The implementation 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.

Defensive priority

Defenders should prioritize verifying exposure of arduino-esp32 installations and upgrading to version 3.3.8 or later.

Recommended defensive actions

• Verify arduino-esp32 installations for exposure
• Upgrade to version 3.3.8 or later
• Monitor for suspicious authentication attempts
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, affected versions, and fixed version. The arduino-esp32 core for ESP32 microcontrollers has a vulnerability in its WebServer Digest authentication implementation prior to version 3.3.8. The implementation 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

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.