Rsync Hostname-based ACL bypass <3.4.3: Auth bypass via PTR
CVE-2026-43617 Published on May 20, 2026
Rsync < 3.4.3 Authorization Bypass via Hostname Resolution
Rsync version 3.4.2 and prior contain an authorization bypass vulnerability in the rsync daemon's hostname-based access control list enforcement when configured with chroot. Attackers can bypass hostname-based deny rules by controlling the PTR record for their source IP address, allowing connections from hostnames that administrators intended to deny when reverse DNS resolution fails and defaults to UNKNOWN.
Vulnerability Analysis
CVE-2026-43617 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality and integrity, and no impact on availability.
Weakness Type
Authentication Bypass by Alternate Name
The software performs authentication based on the name of a resource being accessed, or the name of the actor performing the access, but it does not properly check all possible names for that resource or actor.
Affected Versions
RsyncProject rsync:- Before 3.4.3 is affected.