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Rsync EUVDEUVD-2026-46105

| CVE-2026-44507 MEDIUM
Incorrect Authorization (CWE-863)
2026-07-20 GitHub_M
4.8
CVSS 3.1 · Vendor: GitHub_M
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Severity by source

Vendor (GitHub_M) PRIMARY
4.8 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
vuln.today AI
4.8 MEDIUM

Network-reachable daemon (AV:N), no credentials needed to attempt bypass (PR:N), but AC:H reflects dual prerequisites: PTR record control and a DNS-deficient chroot; scope unchanged and impact limited to module-level file access.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

Lifecycle Timeline

3
Patch available
Jul 20, 2026 - 23:18 EUVD
Analysis Generated
Jul 20, 2026 - 21:35 vuln.today
CVE Published
Jul 20, 2026 - 20:29 cve.org
MEDIUM 4.8

DescriptionCVE.org

Rsync is a file-copying tool that uses a delta-transfer algorithm to synchronize remote and local files. In versions prior to 3.4.3, when using a daemon configured with a chroot, the reverse DNS lookup of the connecting client was performed after the chroot had been entered. If the chroot did not contain the files glibc needs for resolution (/etc/resolv.conf, /etc/nsswitch.conf, /etc/hosts, NSS service modules), the lookup failed and the connecting hostname was set to "UNKNOWN". Hostname-based deny rules ("hosts deny = *.evil.example") therefore could not match, and an attacker who controlled the PTR record for their source IP could connect from a hostname that the administrator had intended to deny. IP-based ACLs ("hosts allow = 10.0.0.0/8") are unaffected. This issue is fixed in version 3.4.3.

AnalysisAI

Rsync daemon before version 3.4.3 allows hostname-based access control rules to be silently bypassed when the daemon is configured with chroot and the chroot directory lacks the files glibc requires for DNS resolution. When resolution fails inside the chroot, the client hostname is set to "UNKNOWN", which never matches administrator-defined "hosts deny" hostname patterns, effectively nullifying those rules. An attacker who controls the PTR record for their source IP can exploit this to connect to an rsync module they were explicitly denied access to; no public exploit code is identified and this is not listed in CISA KEV.

Technical ContextAI

Rsync's daemon mode (rsyncd) supports access control via "hosts allow" and "hosts deny" directives that accept both IP addresses and hostname glob patterns (e.g., "*.evil.example"). When the daemon is configured with "chroot = yes", it calls chroot(2) into the module's path to isolate access. The bug is a sequencing error: the reverse DNS lookup of the connecting client (used to evaluate hostname-based ACL rules) occurs after the chroot has been entered. GNU libc (glibc) requires /etc/resolv.conf, /etc/nsswitch.conf, /etc/hosts, and the relevant NSS service modules to perform name resolution; in hardened or minimal chroot environments these files are deliberately absent. When resolution fails, rsync falls back to the hostname string "UNKNOWN", which does not match any wildcard deny pattern. The root cause is classified as CWE-863 (Incorrect Authorization) - a failure to correctly enforce an authorization decision rather than a missing check. CPE: cpe:2.3:a:rsyncproject:rsync:*:*:*:*:*:*:*:* (all versions prior to 3.4.3). IP-address-based rules parse numeric values before any DNS is attempted and are entirely unaffected.

RemediationAI

The primary fix is to upgrade to Rsync 3.4.3 or later, which resolves the sequencing error by performing the reverse DNS lookup before the chroot is entered, ensuring resolution uses the host system's DNS stack. The vendor advisory detailing this fix is at https://github.com/RsyncProject/rsync/security/advisories/GHSA-rjfm-3w2m-jf4f. If immediate upgrade is not possible, two compensating controls are available: first, replace all hostname-pattern "hosts deny" and "hosts allow" directives with equivalent IP-address or CIDR-range rules (e.g., "hosts deny = 203.0.113.0/24"), since IP-based ACLs are completely unaffected by this issue - the trade-off is that managing large or dynamic IP sets is operationally heavier; second, populate the chroot directory with the minimal DNS resolution files glibc requires (/etc/resolv.conf, /etc/nsswitch.conf, /etc/hosts, and NSS modules such as libnss_dns.so), noting that this increases the chroot's filesystem surface area and partially undermines the isolation benefit of a minimal chroot.

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Micro 5.3 Affected
SUSE Linux Enterprise Micro 5.4 Affected
SUSE Linux Enterprise Micro 5.5 Affected

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EUVD-2026-46105 vulnerability details – vuln.today

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