CVE-2026-70454 in rsync
Summary
by MITRE • 08/13/2026
rsync 3.2.0 through 3.2.3 (openssl mode) and rsync-ssl through 3.4.4 (stunnel mode) contain a TLS certificate validation vulnerability that allows on-path attackers to intercept encrypted sessions by presenting self-signed or otherwise invalid certificates. Attackers can exploit the failure to validate server TLS certificates against a trusted CA or verify certificate hostname matching to decrypt or tamper with rsync session content without detection by the client.
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Analysis
by VulDB Data Team • 08/13/2026
This vulnerability affects rsync implementations in both openssl and stunnel modes, creating a critical security gap that undermines the integrity of encrypted communications. The flaw stems from insufficient TLS certificate validation mechanisms within the rsync protocol implementation, specifically when operating in secure transmission modes. Attackers positioned in network paths between client and server can exploit this weakness by presenting malicious certificates that bypass normal certificate authority verification processes.
The technical execution of this vulnerability relies on the failure to properly validate X509 certificates against trusted certificate authorities as specified in industry standards such as CWE-295. This allows for man-in-the-middle attacks where adversaries can intercept and manipulate rsync session data without client detection. The vulnerability manifests when rsync clients accept connections from servers presenting self-signed certificates or certificates that do not match the expected hostname, creating a trust relationship that should never have been established.
From an operational perspective, this vulnerability poses significant risks to organizations relying on rsync for secure file transfers and synchronization operations. The impact extends beyond simple data interception to include potential data tampering, where attackers can modify transferred files during transit without detection. This represents a fundamental failure in the security model of rsync implementations, as the protocol assumes secure communication channels but fails to validate the authenticity of remote endpoints.
The vulnerability aligns with ATT&CK technique T1041 by enabling unauthorized access to network communications through interception and manipulation of encrypted data flows. Organizations using rsync in production environments face substantial risk exposure, particularly when transferring sensitive or confidential data over untrusted networks. The attack vector requires only basic network position capabilities, making it accessible to a broad range of threat actors.
Mitigation strategies should include immediate upgrading to patched versions of rsync where available, implementing additional network-level security controls such as certificate pinning, and deploying network monitoring solutions to detect anomalous TLS handshake patterns. Organizations should also consider implementing alternative secure file transfer protocols with more robust certificate validation mechanisms, particularly for high-value data transfers. The vulnerability underscores the critical importance of proper certificate validation in cryptographic implementations and highlights the necessity of comprehensive security testing for all components handling encrypted communications.