NLnet Labs Unbound up to and including version 1.25.0 has a denial of service vulnerability in the DNSSEC validator that can lead to a crash given malicious upstream replies. When Unbound constructs chase-reply messages for validation, the code uses the wrong counter to calculate write offsets for ADDITIONAL section rrsets. DNAME duplication could increase the ANSWER section count and authority filtering could decrease the AUTHORITY section count and create an uninitialized array slot. Combining these two, the validator later dereferences this uninitialized pointer, causing an immediate process crash. An adversary controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue records. Unbound 1.25.1 contains a patch with a fix to use the proper counters to calculate the write offsets.

The remote Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8282-1 advisory.

    Andrew Griffiths discovered that Unbound did not properly handle certain DNSCrypt packets. A remote     attacker could possibly use this issue to cause Unbound to crash, resulting in a denial of service.
    (CVE-2026-32792)

    Qifan Zhang discovered that Unbound incorrectly handled DNSSEC validation in certain situations. A remote     attacker could possibly use this issue to execute arbitrary code. This issue only affected Ubuntu 24.04     LTS, Ubuntu 25.10, and Ubuntu 26.04 LTS. (CVE-2026-33278)

    Qifan Zhang discovered that Unbound incorrectly handled certain ghost domain name records. A remote     attacker could possibly use this issue to cause a denial of service. This issue only affected Ubuntu 24.04     LTS, Ubuntu 25.10, and Ubuntu 26.04 LTS. (CVE-2026-40622)

    Qifan Zhang discovered that Unbound did not properly limit processing of long EDNS option lists. A remote     attacker could possibly use this issue to cause Unbound to use excessive resources, leading to a denial of     service. (CVE-2026-41292)

    Qifan Zhang discovered that Unbound incorrectly handled jostle logic under certain circumstances. A remote     attacker could possibly use this issue to cause Unbound to use excessive resources, leading to a denial of     service. (CVE-2026-42534)

    Qifan Zhang discovered that Unbound did not properly bound NSEC3 hash calculations. A remote attacker     could possibly use this issue to cause Unbound to use excessive resources, leading to a denial of service.
    (CVE-2026-42923)

    Qifan Zhang discovered that Unbound incorrectly handled multiple EDNS options in certain situations. A     remote attacker could possibly use this issue to cause Unbound to crash, resulting in a denial of service,     or execute arbitrary code. This issue only affected Ubuntu 24.04 LTS, Ubuntu 25.10, and Ubuntu 26.04 LTS.
    (CVE-2026-42944)

    Qifan Zhang discovered that Unbound incorrectly handled DNSSEC validation of malicious content. A remote     attacker could possibly use this issue to cause Unbound to crash, resulting in a denial of service.
    (CVE-2026-42959)

    TaoFei Guo, Yang Luo, and JianJun Chen discovered that Unbound incorrectly handled delegation processing     in certain situations. A remote attacker could possibly use this issue to poison the DNS cache and obtain     sensitive information. (CVE-2026-42960)

    Qifan Zhang discovered that Unbound did not properly bound name compression in certain cases. A remote     attacker could possibly use this issue to cause Unbound to use excessive resources, leading to a denial of     service. (CVE-2026-44390)

    Qifan Zhang discovered that Unbound had a use-after-free issue in RPZ handling. A remote attacker could     possibly use this issue to cause Unbound to crash, resulting in a denial of service, or execute arbitrary     code. This issue only affected Ubuntu 24.04 LTS, Ubuntu 25.10, and Ubuntu 26.04 LTS. (CVE-2026-44608)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - NLnet Labs Unbound up to and including version 1.25.0 has a denial of service vulnerability in the DNSSEC     validator that can lead to a crash given malicious upstream replies. When Unbound constructs chase-reply     messages for validation, the code uses the wrong counter to calculate write offsets for ADDITIONAL section     rrsets. DNAME duplication could increase the ANSWER section count and authority filtering could decrease     the AUTHORITY section count and create an uninitialized array slot. Combining these two, the validator     later dereferences this uninitialized pointer, causing an immediate process crash. An adversary     controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain     with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue     records. Unbound 1.25.1 contains a patch with a fix to use the proper counters to calculate the write     offsets. (CVE-2026-42959)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
316076	Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS : Unbound vulnerabilities (USN-8282-1)	Nessus	Ubuntu Local Security Checks	critical
315768	Linux Distros Unpatched Vulnerability : CVE-2026-42959	Nessus	Misc.	high

Detections

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CVE-2026-42959

high

Tenable Plugins

critical

high