CVE-2026-40611 HIGH

CVE-2026-40611: Lego: Arbitrary File Write via Path Traversal in Webroot HTTP-01 Provider

Vendor Go-Acme
Product lego
Weakness CWE-22 · Path traversal
Published April 21, 2026
Last update June 30, 2026

CVSS base score

8.8/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction Required
Confidentiality High
Integrity High

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

What the vulnerability does

01Description

Let's Encrypt client and ACME library written in Go (Lego). Prior to 4.34.0, the webroot HTTP-01 challenge provider in lego is vulnerable to arbitrary file write and deletion via path traversal. A malicious ACME server can supply a crafted challenge token containing ../ sequences, causing lego to write attacker-influenced content to any path writable by the lego process. This vulnerability is fixed in 4.34.0.

Key dates

02Disclosure timeline

April 21, 2026 CVE published
June 30, 2026 Record updated