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

Severity: medium (CVSS 4.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-20 · updated 2026-07-24
Weakness: CWE-289

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.

Affected products

RsyncProject rsync: through 3.4.2

References

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

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