CVE-2026-116196 in Rclone
Summary
by MITRE • 10/25/2026
Rclone before v1.75.2 contains a credential exposure vulnerability in the b2 backend that leaks the live account Authorization token and SSE-C keys on HTTP redirects from --b2-download-url hosts. Attackers can observe a same-host HTTPS-to-HTTP downgrade redirect to capture the cleartext B2 token, or receive cross-host redirects disclosing SSE-C customer encryption keys.
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Analysis
by VulDB Data Team • 10/25/2026
The vulnerability identified in Rclone versions prior to 1.75.2 represents a critical credential exposure flaw within its Backblaze B2 backend implementation. This issue stems from improper handling of HTTP redirect responses when interacting with --b2-download-url hosts, leading to the leakage of sensitive authentication tokens and encryption keys. Specifically, the vulnerability allows attackers to capture cleartext Authorization tokens through same-host HTTPS-to-HTTP downgrade redirects or expose SSE-C customer encryption keys via cross-host redirects. This behavior violates fundamental security principles regarding the protection of credentials during network communication transitions and exposes users to significant risk of unauthorized access and data compromise.
From a technical perspective, the flaw occurs when Rclone processes HTTP redirect responses without adequately sanitizing or suppressing sensitive headers that contain authentication details. When an HTTPS connection is downgraded to HTTP via a redirect on the same host, the client inadvertently transmits the B2 Authorization token in cleartext over an unencrypted channel. Similarly, cross-host redirects can disclose SSE-C keys, which are essential for decrypting data stored with server-side encryption where the customer provides their own key. The transmission of these credentials in plaintext allows any network observer or malicious actor positioned within the communication path to intercept and harvest this information. This is particularly dangerous because B2 tokens often grant broad access to cloud storage buckets, while SSE-C keys provide direct decryption capabilities for stored objects.
The operational impact of this vulnerability is severe, as it directly compromises the confidentiality and integrity of data hosted on Backblaze B2 services. An attacker who captures a live account Authorization token can impersonate the legitimate user, gaining full read or write access to associated storage buckets depending on the scope of the leaked credentials. This could lead to unauthorized data exfiltration, modification, or deletion. Furthermore, exposure of SSE-C keys allows an adversary to decrypt sensitive files even if they do not have direct bucket access permissions but can intercept network traffic containing these keys. The risk is amplified in environments where Rclone is used for automated backups or large-scale data transfers, as the volume and frequency of requests increase the window of opportunity for interception attacks such as man-in-the-middle scenarios on unsecured networks.
This vulnerability aligns with CWE-209, which describes the generation of an error message that includes sensitive information about the environment, although in this case it is more accurately categorized under CWE-319: Use of a Cleartext Protocol to Transmit Sensitive Information. The exploitation technique involves manipulating HTTP redirect behaviors to force credential leakage, which maps to ATT&CK tactic T1557, specifically Adversary-in-the-Middle (AitM) or Credential Access via network sniffing during protocol transitions. Organizations relying on Rclone for cloud storage operations must recognize that even minor version updates can introduce significant security regressions if redirect handling is not rigorously tested against credential leakage vectors.
To mitigate this risk, users are strongly advised to upgrade immediately to Rclone version 1.75.2 or later, where the backend logic has been corrected to prevent the transmission of sensitive headers during HTTP redirects. Additionally, administrators should enforce strict HTTPS-only policies for all cloud storage interactions and avoid configuring --b2-download-url hosts that might trigger insecure redirect behaviors. Network-level monitoring can also help detect anomalous traffic patterns indicative of credential interception attempts. Regular auditing of Rclone configurations and keeping software dependencies up to date are essential practices to maintain the security posture of automated data management workflows involving sensitive cloud storage resources.