Vulnerability · Published May 20, 2026 · Assigned by VulnCheck
CVE-2026-43617Rsync < 3.4.3 Authorization Bypass via Hostname Resolution
Medium 4.8
In plain English
A medium-severity security flaw in rsync from RsyncProject. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 21% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.20 | rsync | 3.4.3-r0 | ALPINE-CVE-2026-43617 |
| Alpine:v3.21 | rsync | 3.4.3-r0 | ALPINE-CVE-2026-43617 |
| Alpine:v3.22 | rsync | 3.4.3-r0 | ALPINE-CVE-2026-43617 |
| Alpine:v3.23 | rsync | 3.4.3-r0 | ALPINE-CVE-2026-43617 |
| Alpine:v3.24 | rsync | 3.4.3-r0 | ALPINE-CVE-2026-43617 |
| Debian:12 | rsync | 3.2.7-1+deb12u5 | DEBIAN-CVE-2026-43617 |
| Debian:13 | rsync | 3.4.1+ds1-5+deb13u3 | DEBIAN-CVE-2026-43617 |
| Debian:14 | rsync | 3.4.3+ds1-1 | DEBIAN-CVE-2026-43617 |
| Ubuntu:22.04:LTS | rsync | 3.2.7-0ubuntu0.22.04.6 | UBUNTU-CVE-2026-43617 |
| Ubuntu:24.04:LTS | rsync | 3.2.7-1ubuntu1.4 | UBUNTU-CVE-2026-43617 |
| Ubuntu:25.10 | rsync | 3.4.1+ds1-5ubuntu1.2 | UBUNTU-CVE-2026-43617 |
| Ubuntu:26.04:LTS | rsync | 3.4.1+ds1-7ubuntu0.2 | UBUNTU-CVE-2026-43617 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| RsyncProject | rsync | 0 – before 3.4.3 |
Weakness: CWE-289 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N