CVE-2026-43617Network attack vector

Authorization bypass via failed reverse DNS lookup

Published May 20, 2026 · Updated May 20, 2026

Authorization bypass in the rsync daemon before 3.4.3 allows remote attackers to evade hostname deny rules after reverse DNS failure. The daemon calls client_name() after entering the global daemon chroot; failed name resolution stores UNKNOWN, causing allow_access() hostname patterns to miss. Exposure requires a daemon chroot without resolver support and hostname-based deny rules; affected clients can reach modules intended to reject them.

CVSS severity6.3
Medium
EPSS probability0.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authorization bypass in the rsync daemon before 3.4.3 allows remote attackers to evade hostname deny rules after reverse DNS failure. The daemon calls client_name() after entering the global daemon chroot; failed name resolution stores UNKNOWN, causing allow_access() hostname patterns to miss. Exposure requires a daemon chroot without resolver support and hostname-based deny rules; affected clients can reach modules intended to reject them.

The record

CVE
CVE-2026-43617
Published
May 20, 2026
Updated
May 20, 2026
Vendor
Rsync Project
Product
rsync
Classifications
CWE-289, CWE-863, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 20, 2026CVE publishedPublication date reported by the CVE source.
  2. May 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <3.4.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Rsync Project · rsyncversion=0 <3.4.3

Published CVSS scores

6.3VulnCheckCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
4.8Rsync ProjectCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-289Authentication Bypass by Alternate Name
CWE-863Incorrect Authorization
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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