CVE-2026-40611
Prior to 4.34.0, the webroot HTTP-01 challenge provider in lego is vulnerable to arbitrary file write and deletion via path traversal.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.34%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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
- 8.8 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- EPSS
- 0.34% probability · 27th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-22
- Source
- security-advisories@github.com
References
- 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
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.