Cyber Resilience

CVE-2026-43617

Samba Rsync ≤ 3.4.2

Public PoC
Published
20 May 2026
Modified
24 July 2026
Patch / advisory
View advisory
CVSS Score v4 6.3
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0028 20th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2026-43617 is a medium-severity Authentication Bypass by Alternate Name (CWE-289) vulnerability in Samba Rsync. Its CVSS base score is 6.3 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 20th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and IA-4 (Identifier Management) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A07:2025 Authentication Failures

EU & UK References

Vulnerability Data

Rsync version 3.4.2 and prior contain an authorization bypass vulnerability in the rsync daemon's hostname-based access control list enforcement when configured with chroot. Attackers can bypass hostname-based deny rules by controlling the PTR record for their source IP address, allowing…

more

connections from hostnames that administrators intended to deny when reverse DNS resolution fails and defaults to UNKNOWN.

CWE(s)
CWE-289

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Why these techniques?

Auth bypass in public-facing rsync daemon directly enables T1190 exploitation of remote services via crafted DNS PTR records.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-41035Same product: Samba Rsync
CVE-2026-29518Same product: Samba Rsync
CVE-2026-45232Same product: Samba Rsync
CVE-2026-43619Same product: Samba Rsync
CVE-2026-43620Same product: Samba Rsync
CVE-2026-43618Same product: Samba Rsync
CVE-2025-8415Shared CWE-289
CVE-2025-60375Shared CWE-289
CVE-2025-29266Shared CWE-289
CVE-2026-23903Shared CWE-289

Affected Assets

samba
rsync
≤ 3.4.2

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • AC-3 Access Enforcement
  • IA-4 Identifier Management
  • SC-7 Boundary Protection
Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 8 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V8.3.3
  • V10.3.2
  • V6.4.3

Mitigating Controls (NIST 800-53 r5) AI

AC-3 Access Enforcement good match
prevent

Directly enforces rsync daemon access decisions so that hostname-based deny rules cannot be bypassed by attacker-controlled PTR records.

IA-4 Identifier Management partial match
prevent

Requires proper management and validation of identifiers used for access decisions, preventing reliance on spoofable reverse-DNS hostnames that default to UNKNOWN.

SC-7 Boundary Protection partial match
prevent

Boundary-protection mechanisms can implement IP-based or authenticated allow/deny rules instead of hostname ACLs that are vulnerable to PTR manipulation.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-03 mostly match
prevents

Strong authentication mechanisms directly prevent name-based bypass when they enforce canonical name checks.

PR.AA-01 partial match
prevents

Proper identity management reduces alternate-name collisions but does not guarantee canonicalization inside the auth decision.

PR.AA-05 partial match
prevents

Authorization policy enforcement assumes correct identity; the weakness occurs before policy is applied.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.15 Access control partial match
prevents

Access-control policy can mandate canonical-name checks but does not prescribe the technical implementation.

A.5.16 Identity management partial match
prevents

Identity-management processes can require unique, canonical identifiers, reducing alternate-name bypass risk.

A.5.17 Authentication information partial match
degrades

Proper management of authentication credentials can include rules against duplicate or alias identities.

A.5.18 Access rights partial match
prevents

Access-rights provisioning can enforce canonical-name validation when granting rights.

A.8.3 Information access restriction partial match
prevents

Information-access-restriction mechanisms can implement canonical-name checks to prevent bypass.

A.8.5 Secure authentication partial match
prevents

Secure-authentication controls can require canonical identifiers and reject alternate names.

Hardening callouts derived

Configuration rules from DISA STIG baselines that reduce the attack surface for weaknesses of the type cited by this CVE. Derived transitively via CVE→CWE→STIG over `controls_xwalks` (authoritative rows only).

RHEL 7 (2 rules)
  • V-244557 Red Hat Enterprise Linux operating systems version 7.2 or newer booted with a BIOS must have a unique name for the grub superusers account when booting into single-user and maintenance modes. via CWE-289
  • V-244558 Red Hat Enterprise Linux operating systems version 7.2 or newer booted with United Extensible Firmware Interface (UEFI) must have a unique name for the grub superusers account when booting into single-user mode and maintenance. via CWE-289
RHEL 8 (1 rule)
  • V-244522 RHEL 8 operating systems booted with a BIOS must require a unique superusers name upon booting into single-user and maintenance modes. via CWE-289

References