CVE-2026-116189 in rclone
Summary
by MITRE • 10/25/2026
rclone from 1.55.0 before 1.75.2 contains a signature verification bypass in stable selfupdate that trusts checksums from unsigned bytes preceding the PGP-clearsigned SHA256SUMS block. Attackers controlling the release distribution path can prepend an unsigned checksum line matching a malicious archive, causing selfupdate to install an attacker-controlled rclone executable.
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Analysis
by VulDB Data Team • 10/25/2026
The vulnerability identified in versions of rclone prior to 1.75.2 represents a critical flaw in the integrity verification mechanisms employed during automatic software updates. Specifically, this issue resides within the stable self-update process, which is designed to ensure that users are running unmodified and authentic binaries provided by the official distribution channels. The core technical deficiency lies in how the application parses and validates cryptographic signatures against checksum files. When rclone performs a self-update, it retrieves a SHA256SUMS file that contains hashes for various release artifacts. To verify authenticity, the system relies on PGP-clearsigned blocks within this file. However, the parsing logic fails to strictly isolate the signed content from preceding data. This oversight allows an attacker who controls or can manipulate the release distribution path to inject unsigned bytes before the legitimate PGP-signed block. By prepending a malicious checksum line that corresponds to a compromised archive, the attacker exploits the parser's failure to distinguish between trusted and untrusted sections of the file. Consequently, the self-update mechanism accepts this forged hash as valid because it matches an entry in the list, effectively bypassing the signature verification process entirely.
From a technical perspective, this flaw is classified under CWE-347, which denotes Improper Verification of Cryptographic Signature. The root cause stems from insufficient validation of the data structure's boundaries during the parsing phase. In secure software design, when dealing with clear-signed messages or similar cryptographic constructs, it is imperative to ensure that only the content explicitly enclosed within the signature block contributes to the verification outcome. Here, the application processes checksum lines regardless of their position relative to the PGP signature delimiter. This lack of strict structural validation creates a vector for message injection attacks where an adversary can alter the set of files considered authentic without breaking the cryptographic signature itself. The attacker simply needs to ensure that one of the unsigned entries matches the hash of a malicious binary they have hosted, thereby tricking the updater into downloading and executing code from an untrusted source while believing it is part of the official release package.
The operational impact of this vulnerability is severe, as it directly compromises the integrity and availability of the software ecosystem surrounding rclone. Since self-updates are typically executed with elevated privileges or in contexts where trust is implicitly granted to the update mechanism, a successful exploitation allows for arbitrary code execution on the victim's system. An attacker controlling the distribution path can distribute a malicious version of rclone that may exfiltrate sensitive data stored by users, such as cloud credentials and file paths, or establish persistent backdoors within the user environment. This undermines the fundamental security guarantee provided by digital signatures in software supply chains. Users relying on automatic updates for protection against known vulnerabilities are inadvertently exposed to new threats introduced through this compromised update channel. The trust model of the application is fundamentally broken because the verification step no longer guarantees that the downloaded binary matches the developer's published release.
To mitigate this risk, immediate action must be taken by both developers and end-users. For users currently running affected versions between 1.55.0 and 1.75.2, it is critical to disable automatic self-updates until a patched version can be installed manually from the official website or trusted repositories. Manual verification of checksums using independent sources before installation provides an additional layer of defense against distribution path manipulation. For developers and maintainers of rclone, the primary remediation involves updating the parsing logic in subsequent releases to strictly enforce that only data within the PGP-clearsigned block is considered for signature validation. This requires implementing robust boundary checks to ignore any content preceding the signed section. Furthermore, adopting a more rigorous code review process focused on cryptographic implementation details can prevent similar flaws from being introduced in future updates. Aligning with industry standards such as MITRE ATT&CK technique T1195, which covers Supply Chain Compromise, highlights the importance of securing every link in the delivery chain to maintain user trust and system integrity.