High
Lego: Arbitrary File Write via Path Traversal in Webroot HTTP-01 Provider
Type: advisorySources: OSV
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-40611
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 6 Nov 2026, 01:12 UTC · Revision 1
Source evidence
Lego: Arbitrary File Write via Path Traversal in Webroot HTTP-01 Provider
core-osv · Original sourcePublished 21 Apr 2026, 17:58 UTC
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.
osv:CVE-2026-40611
Complete source record
{
"id": "a917043613355ae9fad34a0e570acd30c93500f46083c7880def1a9db3e79a40",
"url": "https://osv.dev/vulnerability/CVE-2026-40611",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Lego: Arbitrary File Write via Path Traversal in Webroot HTTP-01 Provider",
"summary": "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.",
"evidence": "osv:CVE-2026-40611",
"products": [],
"severity": "high",
"structured": {
"id": "CVE-2026-40611",
"aliases": [
"CVE-2026-40611",
"GHSA-qqx8-2xmm-jrv8",
"GO-2026-5593"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/go-acme/lego",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"fixed": "f3c686a890e6fa36b92614112e8717832894faa7"
}
],
"database_specific": {
"extracted_events": [
{
"range": [
{
"introduced": "0"
},
{
"fixed": "4.34.0"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StringRangeExpression"
},
{
"range": [
{
"introduced": "0"
},
{
"fixed": "4.34.0"
}
],
"source": "DESCRIPTION"
}
]
}
}
],
"versions": [
"v4.33.0",
"v4.32.0",
"v4.31.0",
"v4.30.1",
"v4.29.0",
"v4.28.1",
"v4.28.0",
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"v2.7.1",
"v2.7.0",
"v2.6.0",
"v2.5.0",
"v2.4.0",
"v2.3.0",
"v2.2.0",
"v2.1.0",
"v2.0.1",
"v2.0.0",
"v1.2.1",
"v1.2.0",
"v1.1.0",
"v1.0.1",
"v1.0.0",
"v0.5.0",
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"v0.1.0"
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-40611.json"
}
}
],
"modified": "2026-10-28T02:30:45.590361805Z",
"provider": "osv",
"references": [
"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40611.json",
"https://access.redhat.com/errata/RHSA-2026:21772",
"https://access.redhat.com/security/cve/CVE-2026-40611",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40611.json",
"https://github.com/go-acme/lego/security/advisories/GHSA-qqx8-2xmm-jrv8",
"https://nvd.nist.gov/vuln/detail/CVE-2026-40611",
"https://bugzilla.redhat.com/show_bug.cgi?id=2460233"
],
"provider_metadata": {
"cwe_ids": [
"CWE-22"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40611.json"
}
},
"related_cves": [
{
"value": "CVE-2026-40611",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 513744,
"published_at": "2026-04-21T17:58:35.221+00:00"
}