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

> Attackers can bypass hostname-based access controls in the rsync daemon by manipulating reverse DNS records when chroot is enabled.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 May 2026
- **Updated:** 14 Jul 2026
- **Also known as:** ALPINE-CVE-2026-43617, AZL-86994, BELL-CVE-2026-43617, CLSA-2026-1780945931, CVE-2026-44507, DEBIAN-CVE-2026-43617, ECHO-8072-9059-153b, GHSA-4j4q-473w-9q2r, GHSA-rjfm-3w2m-jf4f, JLSEC-2026-628, UBUNTU-CVE-2026-43617

## 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 (Authentication Bypass by Alternate Name)

## Which versions are affected by CVE-2026-43617?

It affects 1 product.


Products: Samba Rsync.

## How do I fix CVE-2026-43617?

Upgrade to a fixed version.

## 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](https://insights.sbomify.com/CVE-2017-15994/): Security feature bypass in n/a (critical 9.8)
- [CVE-2026-53791](https://insights.sbomify.com/CVE-2026-53791/): rsync < 3.5.0 Daemon IP Spoofing via PROXY Protocol Header (critical 9.1)
- [CVE-2026-70461](https://insights.sbomify.com/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](https://insights.sbomify.com/CVE-2026-70455/): rsync 3.4.2 < 3.5.0 DoS via --zt Zstandard Compression Thread Exhaustion (high 8.7)
- [CVE-2026-70463](https://insights.sbomify.com/CVE-2026-70463/): rsync 3.1.0 < 3.5.0 Authorization Bypass via auth users Directive Parsing (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43617 and fix it if it is affected.

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

Affected product: RsyncProject rsync. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-43617/ (Markdown: https://insights.sbomify.com/CVE-2026-43617/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43617
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43617
- OSV: https://osv.dev/vulnerability/CVE-2026-43617

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43617/
Summaries are generated and may contain mistakes; the official description above is the record.