high8.8
CVE-2026-40611
ACME Lego: Arbitrary File Write via Path Traversal in Webroot HTTP-01 Provider
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| go | github.com/go-acme/lego/v4 | < 4.34.0 | 4.34.0 |
| go | github.com/go-acme/lego/v3 | <= 3.9.0 | none recorded |
| go | github.com/go-acme/lego | <= 2.7.2 | none recorded |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-qqx8-2xmm-jrv8
- https://github.com/go-acme/lego/security/advisories/GHSA-qqx8-2xmm-jrv8
- https://nvd.nist.gov/vuln/detail/CVE-2026-40611
- 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://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40611.json