NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability when handling replies with very large RRsets that Unbound needs to perform name compression for. Malicious upstream responses with very large RRsets with records that don't share a suffix above the root can cause Unbound to spend a considerable time applying name compression to downstream replies. This can lead to degraded performance and eventually denial of service in well orchestrated attacks. An adversary can exploit the vulnerability by querying Unbound for the specially crafted contents of a malicious zone with very large RRsets. Before Unbound replies to the query it will try to apply name compression which was an unbounded operation that could lock the CPU until the whole packet was complete. A compression limit was introduced in 1.21.1 for this but it didn't account for the case where records would not share any suffix above the root. That causes Unbound to go in a different code path because of the compression tree lookup failure and eventually not increment the compression counter for those operations. Unbound 1.25.1 contains a patch with a fix that increments the compression counter regardless of the compression tree lookup. This is a complement fix to CVE-2024-8508.

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 vulnerability when handling replies with very     large RRsets that Unbound needs to perform name compression for. Malicious upstream responses with very     large RRsets with records that don't share a suffix above the root can cause Unbound to spend a     considerable time applying name compression to downstream replies. This can lead to degraded performance     and eventually denial of service in well orchestrated attacks. An adversary can exploit the vulnerability     by querying Unbound for the specially crafted contents of a malicious zone with very large RRsets. Before     Unbound replies to the query it will try to apply name compression which was an unbounded operation that     could lock the CPU until the whole packet was complete. A compression limit was introduced in 1.21.1 for     this but it didn't account for the case where records would not share any suffix above the root. That     causes Unbound to go in a different code path because of the compression tree lookup failure and     eventually not increment the compression counter for those operations. Unbound 1.25.1 contains a patch     with a fix that increments the compression counter regardless of the compression tree lookup. This is a     complement fix to CVE-2024-8508. (CVE-2026-44390)

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
315778	Linux Distros Unpatched Vulnerability : CVE-2026-44390	Nessus	Misc.	medium

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CVE-2026-44390

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medium