# CVE-2026-42855: arduino-esp32: Digest authentication URI mismatch bypass in WebServer allows cross-resource replay attack

> Attackers can bypass per-resource access control in ESP32 WebServer by replaying digest authentication headers for different URIs.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 May 2026
- **Updated:** 13 May 2026
- **Also known as:** GHSA-28hv-fwm3-rpcq

## What is CVE-2026-42855?

CVE-2026-42855 is a high-severity authentication bypass vulnerability in espressif arduino-esp32, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2026-42855?

It affects 1 product.


Products: Espressif Arduino-Esp32.

## How do I fix CVE-2026-42855?

No fix has been published for CVE-2026-42855 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-42855 being exploited?

There is no known exploitation of CVE-2026-42855 in the wild and no public exploit code.

## Other vulnerabilities in espressif arduino-esp32

- [CVE-2026-42854](https://insights.sbomify.com/CVE-2026-42854/): arduino-esp32: Stack buffer overflow in WebServer multipart boundary parsing leads to remote crash potential RCE (critical 9.8)
- [CVE-2026-41429](https://insights.sbomify.com/CVE-2026-41429/): Improper validation of NBNS name_len in arduino-esp32 NetBIOS leads to memory corruption (high 8.8)
- [CVE-2019-12586](https://insights.sbomify.com/CVE-2019-12586/): Denial of service in n/a (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42855 and fix it if it is affected.

What it is: CVE-2026-42855 is a high-severity authentication bypass vulnerability in espressif arduino-esp32, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-42855 in the wild and no public exploit code.

Affected product: espressif arduino-esp32. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-42855/ (Markdown: https://insights.sbomify.com/CVE-2026-42855/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42855
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42855
- OSV: https://osv.dev/vulnerability/CVE-2026-42855

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-42855/
Summaries are generated and may contain mistakes; the official description above is the record.