# CVE-2026-53791: rsync < 3.5.0 Daemon IP Spoofing via PROXY Protocol Header

> Remote attackers can bypass IP-based access controls in rsync daemon by spoofing source IPs via PROXY protocol headers, gaining unauthorized access.

- **Severity:** Critical 9.1 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/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:** 13 Aug 2026
- **Updated:** 14 Aug 2026
- **Also known as:** ALPINE-CVE-2026-53791, AZL-95783, BELL-CVE-2026-53791, DEBIAN-CVE-2026-53791, ECHO-9e2f-c214-61ad, GHSA-h2q9-5fr8-w635, ROOT-OS-DEBIAN-11-CVE-2026-53791, UBUNTU-CVE-2026-53791

## What is CVE-2026-53791?

CVE-2026-53791 is a critical authentication bypass vulnerability in RsyncProject rsync, published on 13 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

rsync daemon before 3.5.0 contains an IP address spoofing vulnerability that allows unauthenticated remote attackers to bypass IP-based access controls by sending a crafted PROXY protocol header with a forged source address. Attackers who can connect directly to the rsync daemon can inject a spoofed source IP in the PROXY protocol header to circumvent hosts allow/deny rules, gaining unauthorized access that would otherwise be blocked based on their real source address.

Weakness: CWE-290 (Authentication Bypass by Spoofing)

## Which versions are affected by CVE-2026-53791?

It affects 1 product.


Products: Samba Rsync.

## How do I fix CVE-2026-53791?

Upgrade to a fixed version.

## Is CVE-2026-53791 being exploited?

There is no known exploitation of CVE-2026-53791 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-2026-70461](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)
- [CVE-2026-53803](https://insights.sbomify.com/CVE-2026-53803/): rsync < 3.5.0 Symlink Following Arbitrary File Overwrite (high 8.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-53791 and fix it if it is affected.

What it is: CVE-2026-53791 is a critical authentication bypass vulnerability in RsyncProject rsync, published on 13 Aug 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-2026-53791 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-2026-53791/ (Markdown: https://insights.sbomify.com/CVE-2026-53791/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53791
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53791
- OSV: https://osv.dev/vulnerability/CVE-2026-53791

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53791/
Summaries are generated and may contain mistakes; the official description above is the record.