CVE-2026-43617

MEDIUM 4.8

Rsync < 3.4.3 Authorization Bypass via Hostname Resolution

CVSS Score

4.8

EPSS Score

0.0%

EPSS Percentile

8th

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.

CWE	CWE-289
Vendor	rsyncproject
Product	rsync
Published	May 20, 2026
Last Updated	May 20, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

None

Affected Versions

RsyncProject / rsync

0 < 3.4.3

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/RsyncProject/rsync/security/advisories/GHSA-rjfm-3w2m-jf4f github.com: https://github.com/RsyncProject/rsync/releases/tag/v3.4.3 vulncheck.com: https://www.vulncheck.com/advisories/rsync-authorization-bypass-via-hostname-resolution

Credits

Joshua Rogers (@MegaManSec)