{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","favicon":"https://feed.craftedsignal.io/favicon-32x32.png","feed_url":"https://feed.craftedsignal.io/products/rclone-v1.75.0-5629f2668c69149bf3d9d8e2a25bb32a2648606e/feed.json","home_page_url":"https://feed.craftedsignal.io/","icon":"https://feed.craftedsignal.io/apple-touch-icon.png","items":[{"_cs_actors":[],"_cs_cpes":["cpe:2.3:a:rclone:rclone:*:*:*:*:*:*:*:*"],"_cs_cves":[{"cvss":9.8,"id":"CVE-2026-88018"}],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["rclone (\u003c 1.75.1)","rclone (v1.70.0 - v1.75.0)","rclone (v1.64.0 - v1.75.0)","rclone (v1.75.0, 5629f2668c69149bf3d9d8e2a25bb32a2648606e)"],"_cs_severities":["critical"],"_cs_tags":["authentication-bypass","s3","rclone","cve-2026-88018","vulnerability","ftp","session-hijacking","authentication","cve-2026-88017","denial-of-service","memory-exhaustion"],"_cs_type":"advisory","_cs_vendors":["rclone"],"content_html":"\u003cp\u003eThe rclone \u003ccode\u003eserve s3\u003c/code\u003e command contains a critical vulnerability (CVE-2026-88018) in its authentication middleware chain. When a user configures \u003ccode\u003erclone serve s3\u003c/code\u003e with the \u003ccode\u003e--auth-proxy\u003c/code\u003e flag but fails to provide an \u003ccode\u003e--auth-key\u003c/code\u003e, the application incorrectly handles the credential registration process. Specifically, the \u003ccode\u003eauthPairMiddleware\u003c/code\u003e parses the \u003ccode\u003eAccessKeyID\u003c/code\u003e directly from the client-controlled \u003ccode\u003eAuthorization\u003c/code\u003e header and registers it into the internal credential store with an empty string as the secret key.\u003c/p\u003e\n\u003cp\u003eBecause an empty string is a valid HMAC key for SigV4, any network-reachable attacker can compute a valid signature for an arbitrary \u003ccode\u003eAccessKeyID\u003c/code\u003e using an empty secret. The application subsequently accepts these forged signatures as authenticated requests. This effectively bypasses all authentication for the S3 interface, granting attackers the ability to interact with the backend as any identity accepted by the configured auth-proxy script. This vulnerability affects all rclone versions prior to 1.75.1.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eAttacker identifies a network-accessible rclone instance running \u003ccode\u003eserve s3\u003c/code\u003e with \u003ccode\u003e--auth-proxy\u003c/code\u003e enabled.\u003c/li\u003e\n\u003cli\u003eAttacker verifies the configuration lacks an \u003ccode\u003e--auth-key\u003c/code\u003e (often inferred by testing unauthorized access).\u003c/li\u003e\n\u003cli\u003eAttacker selects an arbitrary \u003ccode\u003eAccessKeyID\u003c/code\u003e to impersonate a target user or administrative account.\u003c/li\u003e\n\u003cli\u003eAttacker constructs an S3 API request (e.g., \u003ccode\u003eListAllMyBuckets\u003c/code\u003e) using the chosen \u003ccode\u003eAccessKeyID\u003c/code\u003e.\u003c/li\u003e\n\u003cli\u003eAttacker computes a valid SigV4 signature for the request payload using an empty string as the secret key.\u003c/li\u003e\n\u003cli\u003eAttacker sends the forged request to the rclone instance.\u003c/li\u003e\n\u003cli\u003eThe \u003ccode\u003eauthPairMiddleware\u003c/code\u003e registers the attacker-supplied key with an empty secret in the internal store.\u003c/li\u003e\n\u003cli\u003eThe gofakes3 handler validates the forged signature against the registered empty secret, granting full access to the requested S3 backend.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eSuccessful exploitation allows unauthenticated remote attackers to gain full access to the S3 interface of an rclone instance. This can lead to unauthorized data exfiltration, deletion, or modification of stored objects, depending on the permissions of the identities handled by the auth-proxy script. No prior credentials or user interaction are required for exploitation.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eUpgrade rclone to version 1.75.1 or later immediately to apply the fix that prevents the server from starting with an insecure configuration.\u003c/li\u003e\n\u003cli\u003eAudit existing rclone deployments for the usage of \u003ccode\u003e--auth-proxy\u003c/code\u003e in \u003ccode\u003eserve s3\u003c/code\u003e commands.\u003c/li\u003e\n\u003cli\u003eEnsure that all \u003ccode\u003eserve s3\u003c/code\u003e instances utilizing \u003ccode\u003e--auth-proxy\u003c/code\u003e are configured with a robust \u003ccode\u003e--auth-key\u003c/code\u003e if immediate upgrading is not feasible, although upgrading is the only supported mitigation.\u003c/li\u003e\n\u003cli\u003eReview logs for S3 requests that appear to be authenticated using anomalous or unknown \u003ccode\u003eAccessKeyID\u003c/code\u003e values.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-09-11T00:54:01Z","date_published":"2026-09-11T00:53:08Z","id":"https://feed.craftedsignal.io/briefs/2026-09-rclone-auth-bypass/","summary":"A critical authentication bypass vulnerability in rclone's S3 serving mode allows unauthenticated attackers to spoof identity via forged SigV4 signatures when '--auth-proxy' is used without '--auth-key'.","title":"SigV4 Authentication Bypass in rclone serve s3","url":"https://feed.craftedsignal.io/briefs/2026-09-rclone-auth-bypass/"}],"language":"en","title":"CraftedSignal Threat Feed - Rclone (V1.75.0, 5629f2668c69149bf3d9d8e2a25bb32a2648606e)","version":"https://jsonfeed.org/version/1.1"}