# CVE-2026-40611: golang-github-xenolf-lego: Let's Encrypt client and ACME library written in Go (Lego)

CVE-2026-40611 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-40611, released April 21, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-40611
- Priority: High
- CVSS: 8.8 (high)
- EPSS: 0.0042
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 21, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | golang-github-xenolf-lego Debian 14 | 4.35.2-1 | [DEBIAN-CVE-2026-40611](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40611.md) | Apr 21, 2026 |
| Linux | govulncheck-vulndb opensuse-leap 16.0 | 0.0.20260727T201416-160000.1.1 | [OPENSUSE-SU-2026:21551-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21551-1.md) | Aug 10, 2026 |
| Linux | govulncheck-vulndb sles 16.0 | 0.0.20260727T201416-160000.1.1 | [SUSE-SU-2026:23227-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23227-1.md) | Aug 10, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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