CVE-2026-88018
CRITICAL · 9.8 EPSS 0.5%Real vuln + patch, but "public exploit" claim unverified; no KEV; feed-driven repetition dominates chatter.
What: rclone serve s3 with --auth-proxy but without --auth-key allows SigV4 signature bypass, enabling unauthenticated attackers to impersonate any access key and reach backend storage. CVSS 9.8 CRITICAL.
Why it matters: Published yesterday; NVD confirms authentication bypass in production configurations. Posts claim "public exploit" exists, but metadata lacks KEV listing or confirmed PoC links. Vendor (rclone team) has issued fix (v1.75.1) same day, signaling urgent patching. Real vuln affecting cloud sync workflows, but social signal is largely automated feed repetition.
Where it's seen: Six near-identical posts from a vulnerability feed (ABYSSAL) amplifying the CVSS score and claiming public exploit without substantiating links. One additional post from another feed. No defender triage questions, no independent researcher confirmation yet.
RISK: CRITICAL — Unauthenticated auth bypass in cloud-facing tool; vendor patched same day; affects deployed --auth-proxy configs.
Description
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.
CVSS 3.1 breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H- Attack vector
- Network
- Complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High