CVE-2026-40611
ACME Lego: Arbitrary File Write via Path Traversal in Webroot HTTP-01 Provider
8.8
HIGH
CVSS 3.1
EPSS 0.05%
Description
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.
How to fix CVE-2026-40611
To remediate CVE-2026-40611, upgrade the affected package to a fixed version below.
- —no fix listed
- —no fix listed
- —no fix listed
- —upgrade to 4.34.0 or later
Is CVE-2026-40611 being exploited?
Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.
Affected packages (4)
- from 0
- from 0, <= 2.7.2
- from 0, <= 3.9.0
- from 0, < 4.34.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH8.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H |