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PatchSiren cyber security CVE debrief

CVE-2026-53791 RsyncProject CVE debrief

The CVE-2026-53791 record indicates an IP address spoofing vulnerability in rsync daemon before version 3.5.0, allowing unauthenticated remote attackers to bypass IP-based access controls. This vulnerability can be exploited by attackers who can connect directly to the rsync daemon, allowing them to 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. The vulnerability is due to improper handling of the PROXY protocol header. Evidence is based on official CVE and NVD records, as well as vendor advisories. System administrators and security teams should review the official CVE and NVD records for further details.

Vendor
RsyncProject
Product
rsync
CVSS
CRITICAL 9.1
CISA KEV
Not listed in stored evidence
Original CVE published
2026-08-13
Original CVE updated
2026-08-26
Advisory published
2026-08-13
Advisory updated
2026-08-26

Who should care

System administrators and security teams responsible for rsync daemon installations, particularly those using versions before 3.5.0, should be aware of this vulnerability and take steps to mitigate it.

Technical summary

The rsync daemon before version 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. This vulnerability can be exploited by attackers who can connect directly to the rsync daemon, allowing them to 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.

Defensive priority

Organizations using rsync daemon versions before 3.5.0 should prioritize upgrading to version 3.5.0 or later to mitigate the IP address spoofing vulnerability.

Recommended defensive actions

  • Upgrade rsync daemon to version 3.5.0 or later
  • Implement additional monitoring and logging to detect potential exploitation attempts
  • Review and update IP-based access controls to ensure they are not solely relied upon for security
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE-2026-53791 record indicates an IP address spoofing vulnerability in rsync daemon before version 3.5.0, allowing unauthenticated remote attackers to bypass IP-based access controls. The vulnerability is due to improper handling of the PROXY protocol header. Evidence is based on official CVE and NVD records, as well as vendor advisories.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-53791 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-53791

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-53791 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-53791

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.