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Vulnerability record · CVE-2026-40611 · published 21 April 2026

CVE-2026-40611: Path traversal vulnerability

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.

8.8 CVSS 3.1 High EPSS 0.55% · top 56.5% CWE-22 · Path traversal Deferred
8.8CVSS 3.1 base score
0.55%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
6References
15 Jul 2026Last modified by NVD

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.

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

References

LinkTags
https://github.com/go-acme/lego/security/advisories/GHSA-qqx8-2xmm-jrv8
https://access.redhat.com/errata/RHSA-2026:21772
https://access.redhat.com/security/cve/CVE-2026-40611
https://bugzilla.redhat.com/show_bug.cgi?id=2460233
https://github.com/go-acme/lego/security/advisories/GHSA-qqx8-2xmm-jrv8
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40611.json

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Source: NIST National Vulnerability Database (record CVE-2026-40611), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.