CVE-2026-77375 in SFTPGo
Summary
by MITRE • 10/13/2026
SFTPGo is an open source, event-driven file transfer solution. Prior to 2.7.5, an authenticated SSH user can send a malformed protocol message while opening a channel, causing an unhandled error that terminates the server process and affects all connected users until restart. No confidentiality or integrity impact has been identified. This issue is fixed in 2.7.5.
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Analysis
by VulDB Data Team • 10/13/2026
SFTPGo represents a significant open-source solution for event-driven file transfer operations, leveraging SSH protocols to facilitate secure data exchange between clients and servers. The architecture relies heavily on the stability of its underlying SSH implementation to maintain continuous availability for multiple concurrent users. In versions prior to 2.7.5, a critical reliability flaw exists within the server's handling of channel initialization sequences during authenticated sessions. This vulnerability stems from an insufficient validation mechanism when processing incoming protocol messages associated with opening new channels. Specifically, if an authenticated user transmits a malformed or structurally invalid message during this handshake phase, the application fails to gracefully handle the exception. Instead of isolating the error and rejecting the specific connection attempt, the unhandled error propagates up the call stack, resulting in a fatal panic that terminates the entire server process.
The operational impact of this vulnerability is primarily centered on service availability rather than data security. Because the SFTPGo daemon crashes upon receiving such malformed input from any single authenticated user, all active connections are immediately severed. This results in a denial-of-service condition where legitimate users lose access to file transfer services until an administrator manually restarts the server process. While this disruption can severely impact business continuity and operational workflows, it is important to note that no confidentiality or integrity compromises have been identified. The attacker cannot exploit this flaw to read sensitive files, modify existing data, or escalate privileges beyond their authenticated session level. The primary risk remains the potential for repeated service outages if an adversary discovers a reliable method to trigger this condition repeatedly.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the server fails to adequately sanitize and verify the structure of incoming protocol messages before processing them. Furthermore, it maps directly to MITRE ATT&CK technique T1499 Endpoint Denial of Service, specifically under sub-techniques involving application exhaustion or resource consumption through malformed inputs. The attack vector requires authentication, which classifies this as an authenticated remote denial-of-service vulnerability. This requirement limits the scope of potential attackers but does not eliminate the risk for environments where internal users may have malicious intent or compromised credentials.
Mitigation strategies focus on upgrading to version 2.7.5 or later, where the developers have implemented robust error handling and input validation routines that prevent malformed messages from causing a server-wide crash. In scenarios where immediate patching is not feasible, organizations should consider implementing network-level controls such as rate limiting for SSH connections to reduce the frequency of channel initiation attempts. Additionally, deploying an intrusion detection system capable of identifying anomalous protocol behavior can help in monitoring for potential exploitation attempts. Regular security audits and adherence to secure coding practices that emphasize defensive programming against malformed inputs are essential long-term measures to prevent similar availability issues in critical file transfer infrastructure.