The version of unbound installed on the remote host is prior to 1.17.0-2. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2UNBOUND-1.17-2026-008 advisory.

    NLnet Labs Unbound 1.19.1 up to and including version 1.25.0 has a vulnerability in the DNSSEC validator     that enables denial of service and possible remote code execution as a result of deep copying a data     structure and erroneously overwriting a destination pointer. An adversary can exploit the vulnerability by     controlling a malicious signed zone and querying a vulnerable Unbound. When DS sub-queries need to suspend     validation due to NSEC3 computational budget exhaustion (introduced in Unbound 1.19.1), Unbound deep-     copies response messages to preserve them across memory region teardown. A struct-assignment bug     overwrites the destination's pointer with the source's pointer. After the sub-query region is freed, the     resumed validator dereferences this dangling pointer, triggering a crash or potentially enabling arbitrary     code execution. Unbound 1.25.1 contains a patch with a fix to preserve the correct pointer when deep     copying the data structure. (CVE-2026-33278)

    NLnet Labs Unbound 1.16.2 up to and including version 1.25.0 has a vulnerability of the 'ghost domain     names' family of attacks that could extend the ghost domain window by up to one cached TTL configured     value. Similar to other 'ghost domain names' attacks, an adversary needs to control a (ghost) zone and be     able to query a vulnerable Unbound. A single client NS query can cause Unbound to overwrite the cached     expired parent-side referral NS rrset with the child-side apex NS rrset and essentially extend the ghost     domain window by up to one cached TTL configured value ('cache-max-ttl'). In configurations where 'harden-     referral-path: yes' is used (non-default configuration), no client NS query is required since Unbound     implicitly performs that query. Unbound 1.25.1 contains a patch with a fix that does not allow extension     of TTLs for (parent) NS records regardless of their trust. (CVE-2026-40622)

    NLnet Labs Unbound up to and including version 1.25.0 is vulnerable to a degradation of service attack     related to parsing long lists of incoming EDNS options. An adversary sending queries with too many EDNS     options can hold Unbound threads hostage while they are parsing and creating internal data structures for     the options. Coordinated attacks can result in degradation and/or denial of service. Unbound 1.25.1     contains a patch with a fix to limit acceptable incoming EDNS options (100). (CVE-2026-41292)

    NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the jostle logic that could     defeat its purpose and degrade resolution performance. Retransmits of the same query could renew the age     of slow running queries and not allow the jostle logic to see them as aged and potential targets for     replacement with new queries. An adversary who can query a vulnerable Unbound and who can control a domain     name server that replies slowly and/or maliciously to Unbound's queries can exploit the vulnerability and     degrade the resolution performance of Unbound. When Unbound's 'num-queries-per-thread' reaches its limit,     the jostle logic kicks in. When a new query comes in, half of the available queries that are also slow to     resolve are candidates for replacement. The vulnerability then happens because duplicate queries that need     resolution would skew the aging result by using the timestamp of the latest duplicate query instead of the     original one that started the resolution effort. Cache and local data response performance remains     unaffected. Coordinated attacks could raise this to a denial of resolution service. Unbound 1.25.1     contains a patch with a fix to attach an initial, non-updatable start time for incoming queries that allow     the jostle logic to work as intended. (CVE-2026-42534)

    NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where     the code path to consult the negative cache for DS records does not take into account the limit on NSEC3     hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An     adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably     high iterations for child delegations and querying a vulnerable Unbound. Unbound will keep performing the     allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in     1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the     hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise     the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable     code path with the existing limit for NSEC3 hash calculations. (CVE-2026-42923)

    NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap     overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply     packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for     the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by     attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the     size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the     available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data     and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a     fix to prevent truncation of the EDNS field size calculation. (CVE-2026-42944)

    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)

    NLnet Labs Unbound up to and including version 1.25.0 is vulnerable to poisoning via promiscuous records     for the authority section. Promiscuous RRSets that complement DNS replies in the authority section can be     used to trick Unbound to cache such records. If an adversary is able to attach such records in a reply     (i.e., spoofed packet, fragmentation attack) he would be able to poison Unbound's cache. A malicious actor     can exploit the possible poisonous effect by injecting RRSets other than NS that are also accompanied by     address records in a reply, for example MX. This could be achieved by trying to spoof a reply packet or     fragmentation attacks. Unbound would then accept the relative address records in the additional section     and cache them if the authority RRSet has enough trust at this point, i.e., in-zone data for the     delegation point. Unbound 1.25.1 contains a patch with a fix that disregards address records from the     additional section if they are not explicitly relevant only to authority NS records, mitigating the     possible poison effect. This is a complement fix to CVE-2025-11411. (CVE-2026-42960)

    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)

    NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a locking inconsistency vulnerability     that when certain conditions are met (multi-threaded, RPZ XFR reload, RPZ zone with 'rpz-nsip'/'rpz-     nsdname' triggers) it could result in heap use-after-free and eventual crash. An adversary can exploit the     vulnerability if conditions are first met on a vulnerable Unbound, i.e., multi-threaded, an RPZ zone with     'rpz-nsip'/'rpz-nsdname' triggers and an ongoing XFR for that RPZ zone. Local RPZ files do not trigger the     vulnerability. If the timing is right and an XFR happens at the same time another thread needs to read     that RPZ zone, the reader may not hold the lock long enough and the thread applying the XFR may free     objects that the reader is about to walk causing the use-after-free. Unbound 1.25.1 contains a patch with     a fix to the locking code. (CVE-2026-44608)

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

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

Detections

Analytics

Amazon Linux 2 : unbound, --advisory ALAS2UNBOUND-1.17-2026-008 (ALASUNBOUND-1.17-2026-008)

critical Nessus Plugin ID 328496

Version 1.2

Version 1.1

Version 1.2 Aug 31, 2026, 4:25 PM CVSS metrics ("Cvssv4 supplemental" set to "CVSS:4.0/U:Red") Plugin Feed: 202608311625
Version 1.1 Jul 21, 2026, 8:31 PM New Plugin Feed: 202607212031