CVE-2026-40611
High
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.
SeverityHigh
CVSS8.8
Exploit probability—
ProductGithub.com/go-acme/lego/v4
PublishedApr 21, 2026
First seenApr 21, 2026
Weakness typeCWE-22Path traversal
How to fix
Update
- github.com/go-acme/lego/v44.34.0 or later
Vendor advisories
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| github.com/go-acme/lego/v4Go | v < 4.34.0 | 4.34.0 |
| github.com/go-acme/lego/v3Go | v ≤ 3.9.0 | — |
| github.com/go-acme/legoGo | v ≤ 2.7.2 | — |
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