rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass
rclone is a command-line program to sync files and directories to and from different cloud storage providers. Prior to 1.75.1, rclone serve s3 configured with --auth-proxy but without --auth-key allows authPairMiddleware to register any client-chosen accessKeyID with an empty ws.s3Secret. gofakes3 then verifies the request’s SigV4 signature against that same empty secret, while Server.auth passes the access key identifier as both the user and authentication value to the proxy without an independent per-identity secret. An unauthenticated network attacker can therefore choose an arbitrary access key, sign with an empty secret, and reach whatever backend the auth-proxy script resolves for that identity. This issue is fixed in version 1.75.1.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-88018
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 2 Nov 2026, 19:12 UTC · Revision 1
Source evidence
rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass
core-osv · Original sourcePublished 10 Sept 2026, 16:03 UTC
rclone is a command-line program to sync files and directories to and from different cloud storage providers. Prior to 1.75.1, rclone serve s3 configured with --auth-proxy but without --auth-key allows authPairMiddleware to register any client-chosen accessKeyID with an empty ws.s3Secret. gofakes3 then verifies the request’s SigV4 signature against that same empty secret, while Server.auth passes the access key identifier as both the user and authentication value to the proxy without an independent per-identity secret. An unauthenticated network attacker can therefore choose an arbitrary access key, sign with an empty secret, and reach whatever backend the auth-proxy script resolves for that identity. This issue is fixed in version 1.75.1.
osv:CVE-2026-88018
Complete source record
{
"id": "83b7665742c7c2eecff8cc4a14e83be76c54e2f49ce0f0a0e382be4ea05db26f",
"url": "https://osv.dev/vulnerability/CVE-2026-88018",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass",
"summary": "rclone is a command-line program to sync files and directories to and from different cloud storage providers. Prior to 1.75.1, rclone serve s3 configured with --auth-proxy but without --auth-key allows authPairMiddleware to register any client-chosen accessKeyID with an empty ws.s3Secret. gofakes3 then verifies the request’s SigV4 signature against that same empty secret, while Server.auth passes the access key identifier as both the user and authentication value to the proxy without an independent per-identity secret. An unauthenticated network attacker can therefore choose an arbitrary access key, sign with an empty secret, and reach whatever backend the auth-proxy script resolves for that identity. This issue is fixed in version 1.75.1.",
"evidence": "osv:CVE-2026-88018",
"products": [],
"severity": "critical",
"structured": {
"id": "CVE-2026-88018",
"aliases": [
"BIT-rclone-2026-88018",
"CVE-2026-88018",
"GHSA-xwwr-4h3p-r22c",
"GO-2026-6462"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/rclone/rclone",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"fixed": "687d264b689b8c49a67e2e52a8a5e0caa01c04ce"
},
{
"fixed": "90595f34f27f569be6b27c57fe5ab65057d323bd"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:rclone:rclone:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "0"
},
{
"fixed": "1.75.1"
}
],
"source": "CPE_RANGE"
},
{
"range": [
{
"fixed": "90595f34f27f569be6b27c57fe5ab65057d323bd"
}
],
"source": "REFERENCES_COMMIT"
},
{
"range": [
{
"fixed": "687d264b689b8c49a67e2e52a8a5e0caa01c04ce"
}
],
"source": "REFERENCES_TAG",
"original_tag": "v1.75.1"
}
]
}
}
],
"versions": [
"v1.75.0",
"v1.74.0",
"v1.73.0",
"v1.72.0",
"v1.71.0",
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"v1.37",
"v1.36",
"v1.35",
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"v1.29-1-gbb75d80",
"v1.29",
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"v1.23",
"v1.22",
"v1.21",
"v1.20",
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"v1.17",
"v1.16",
"v1.15",
"v1.14",
"v1.13",
"v1.12",
"v1.11",
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"v1.08",
"v1.07",
"v1.06",
"v1.05",
"v1.04",
"v1.03",
"v1.01",
"v1.00",
"v0.99",
"v0.98",
"v0.97",
"v0.96",
"v0.95",
"v0.94",
"v0.93",
"v0.92",
"v0.91",
"v0.90"
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-88018.json"
}
}
],
"modified": "2026-10-28T02:30:22.886790150Z",
"provider": "osv",
"references": [
"https://github.com/rclone/rclone/releases/tag/v1.75.1",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/88xxx/CVE-2026-88018.json",
"https://github.com/rclone/rclone/security/advisories/GHSA-xwwr-4h3p-r22c",
"https://nvd.nist.gov/vuln/detail/CVE-2026-88018",
"https://github.com/rclone/rclone/commit/90595f34f27f569be6b27c57fe5ab65057d323bd"
],
"provider_metadata": {
"cwe_ids": [
"CWE-287",
"CWE-306"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/88xxx/CVE-2026-88018.json"
}
},
"related_cves": [
{
"value": "CVE-2026-88018",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 489014,
"published_at": "2026-09-10T16:03:25.692+00:00"
}