CVE-2026-53791: CWE-290 Authentication Bypass by Spoofing in RsyncProject rsync
A critical authentication bypass vulnerability exists in rsync daemon versions up to 3.4.4. This flaw allows unauthenticated remote attackers to bypass IP-based access controls by sending a crafted PROXY protocol header with a spoofed source IP address. Exploiting this, attackers can circumvent host allow/deny rules and gain unauthorized access to the rsync daemon.
AI Analysis
Technical Summary
The rsync daemon before version 3.5.0 contains an IP address spoofing vulnerability (CVE-2026-53791) that enables unauthenticated remote attackers to bypass IP-based access controls. By sending a specially crafted PROXY protocol header with a forged source address, an attacker who can connect directly to the rsync daemon can inject a spoofed source IP. This allows the attacker to circumvent hosts allow/deny rules that rely on the real source IP, thereby gaining unauthorized access that would otherwise be blocked.
Potential Impact
Attackers can bypass IP-based access control mechanisms on the rsync daemon, potentially gaining unauthorized access to resources protected by host allow/deny rules. This can lead to unauthorized data access or manipulation depending on the rsync daemon's configuration and usage.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, consider restricting network access to the rsync daemon to trusted hosts only and disabling the PROXY protocol if it is not required.
CVE-2026-53791: CWE-290 Authentication Bypass by Spoofing in RsyncProject rsync
Description
A critical authentication bypass vulnerability exists in rsync daemon versions up to 3.4.4. This flaw allows unauthenticated remote attackers to bypass IP-based access controls by sending a crafted PROXY protocol header with a spoofed source IP address. Exploiting this, attackers can circumvent host allow/deny rules and gain unauthorized access to the rsync daemon.
CVSS v4.0
Score 9.1critical
Affected software
RsyncProject
rsync
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The rsync daemon before version 3.5.0 contains an IP address spoofing vulnerability (CVE-2026-53791) that enables unauthenticated remote attackers to bypass IP-based access controls. By sending a specially crafted PROXY protocol header with a forged source address, an attacker who can connect directly to the rsync daemon can inject a spoofed source IP. This allows the attacker to circumvent hosts allow/deny rules that rely on the real source IP, thereby gaining unauthorized access that would otherwise be blocked.
Potential Impact
Attackers can bypass IP-based access control mechanisms on the rsync daemon, potentially gaining unauthorized access to resources protected by host allow/deny rules. This can lead to unauthorized data access or manipulation depending on the rsync daemon's configuration and usage.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, consider restricting network access to the rsync daemon to trusted hosts only and disabling the PROXY protocol if it is not required.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- VulnCheck
- Date Reserved
- 2026-06-10T20:14:32.827Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6a7ddec4bf8831d5395cfc97
Added to database: 08/13/2026, 15:12:04 UTC
Last enriched: 08/21/2026, 13:30:47 UTC
Last updated: 09/28/2026, 13:47:45 UTC
Views: 58
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