CVE-2026-43617 Rsync < 3.4.3 Authorization Bypass via Hostname Resolution

What is CVE-2026-43617?

CVE-2026-43617 is a medium-severity authentication bypass vulnerability in RsyncProject rsync, published on 20 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

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.

Weakness: CWE-289

Which versions are affected by CVE-2026-43617?

It affects 1 product.

Products include Samba Rsync.

How do I fix CVE-2026-43617?

Upgrade to a fixed version.

Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.

Is CVE-2026-43617 being exploited?

There is no known exploitation of CVE-2026-43617 in the wild and no public exploit code.

Other vulnerabilities in RsyncProject rsync

• CVE-2017-15994 Security feature bypass in n/a Critical 9.8
• CVE-2026-53791 rsync < 3.5.0 Daemon IP Spoofing via PROXY Protocol Header Critical 9.1
• CVE-2026-70461 rsync 3.2.5 < 3.5.0 Heap Out-of-Bounds Write via files-from Entry High 8.8
• CVE-2026-70455 rsync 3.4.2 < 3.5.0 DoS via --zt Zstandard Compression Thread Exhaustion High 8.7
• CVE-2026-70463 rsync 3.1.0 < 3.5.0 Authorization Bypass via auth users Directive Parsing High 8.6

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• GitHub advisory
• How this page is made

Also known as ALPINE-CVE-2026-43617, AZL-86994, BELL-CVE-2026-43617, CLSA-2026-1780945931, CVE-2026-44507, DEBIAN-CVE-2026-43617 and 5 more.