SB2026082634 - Multiple vulnerabilities in NSD

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Main Vulnerability Database SB2026082634

SB2026082634 - Multiple vulnerabilities in NSD

Published: August 26, 2026

Security Bulletin ID SB2026082634
CSH Severity
Medium
Patch available
YES
Number of vulnerabilities 4
Exploitation vector Remote access
Highest impact Denial of service

Breakdown by Severity

Medium 75% Low 25%
  • Low
  • Medium
  • High
  • Critical

Description

This security bulletin contains information about 4 vulnerabilities.


1) Improper access control (CVE-ID: CVE-2026-18664)

CWE-ID: CWE-284 - Improper Access Control

CVSSv4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]


The vulnerability allows a remote attacker to bypass IP-based access control restrictions.

The vulnerability exists due to improper access control in IP range access control handling when comparing IP addresses against configured ranges on little endian systems. A remote attacker can send requests from unintended IP addresses to bypass IP-based access control restrictions.

The issue affects both IPv4 and IPv6 range comparisons.


2) Improper Resource Shutdown or Release (CVE-ID: CVE-2026-18916)

CWE-ID: CWE-404 - Improper Resource Shutdown or Release

CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]


The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to improper handling of throttled tcp receive windows in serve child processing when handling a tcp query followed by a reduced tcp receive window. A remote attacker can throttle the tcp receive window down to 1 after sending a tcp query to cause a denial of service.

By repeatedly crashing serve child processes, all tcp service to the affected instance can be denied.


3) Input validation error (CVE-ID: CVE-2026-19401)

CWE-ID: CWE-20 - Improper input validation

CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]


The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to improper input validation in the NSD server child process when handling specially crafted UDP DNS queries with multiple DNS Cookie options. A remote attacker can send a specially crafted query to cause a denial of service.

Only debugging or non-release builds are vulnerable, and sustained exploitation can severely hamper service or deny DNS service.


4) Improper access control (CVE-ID: CVE-2026-19538)

CWE-ID: CWE-284 - Improper Access Control

CVSSv4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:H/VA:N/SC:N/SI:N/SA:N]


The vulnerability allows a remote user to bypass IP-based access controls.

The vulnerability exists due to improper access control in the proxy protocol port handling when processing a repeated query over a kept-open TCP or TLS connection. A remote user can send the same query twice on a persistent connection to bypass IP-based access controls.

This issue affects BLOCKED access control list items and may allow spoofing of arbitrary IP addresses for queries, transfers, and notifies.


Remediation

Install update from vendor's website.

References