Detections
Analytics
Amazon Linux 2 : unbound (ALASUNBOUND-1.17-2026-011)
critical Nessus Plugin ID 351053
Synopsis
The remote Amazon Linux 2 host is missing a security update.Description
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-1.17-2026-011 advisory.In NLnetLabs Unbound up to and including 1.26.0, a degradation of service vulnerability is present in the TCP/DoT reading procedure where there is no limit on consecutive reads. A malicious actor that can stream and sustain a rate of distinct uncached names over the TCP/DoT connection, monopolizes a single worker's entire event loop for as long as its writes stay ahead of the drain. (CVE-2026-80225)
In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability. (CVE-2026-81634)
In NLnet Labs Unbound up to and including 1.26.0, a vulnerability was found in that can progressively corrupt heap memory and under certain systems and compilation options could lead to remote code execution.
The vulnerability starts when CNAME synthesis during an upstream response needs to enforce(rewrite) a max TTL value in the packet buffer. Coupled with a compression pointer that points to the overwritten value and invalidates the domain name, it leads to an error path that does not properly move the buffer position and allows for the heap buffer overflow. Since this is heavily reliant on heap memory layout, results are memory corruption that eventually leads to a crash and under specific systems and compilation options remote code execution. (CVE-2026-82717)
Novel vulnerabilities to launch algorithmic complexity attacks on DNSSEC have been researched under the term 'ReTrap'. These result in degradation of service when malicious zones are used to serve the algorithmic complexity vulnerabilities. NLnet Labs Unbound up to and including 1.26.0 is vulnerable to some of them. TagTrap, where the triple(Zone, Algo, KeyTag) matching mechanism introduces a significant attack vector when resolvers handle malicious responses containing numerous mismatched DNSKEY, RRSIG, and DS record. DelegationTrap, where constructing the chain-of-trust requires iterative validation of DNSKEY and DS records from the root zone downward. For deeply nested domains, this results in significant computational overhead. NsecTrap, where responses with excessive invalid NSEC records compel the resolver to validate each one. AdditionalTrap, where Unbound by default would try to DNSSEC validate the ADDITIONAL section as well. This can be exploited to waste validation resources by malicious users. (CVE-2026-85501)
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.
Solution
Run 'yum update unbound' or or 'yum update --advisory ALAS2UNBOUND-1.17-2026-011' to update your system.See Also
https://alas.aws.amazon.com//AL2/ALAS2UNBOUND-1.17-2026-011.html
https://alas.aws.amazon.com/faqs.html
https://explore.alas.aws.amazon.com/CVE-2026-80225.html
https://explore.alas.aws.amazon.com/CVE-2026-81634.html
Plugin Details
Severity: Critical
ID: 351053
File Name: al2_ALASUNBOUND-1_17-2026-011.nasl
Version: 1.1
Type: Local
Agent: unix
Published: 9/29/2026
Updated: 9/29/2026
Supported Sensors: Nessus Agent, Continuous Assessment, Nessus
Risk Information
VPR
Risk Factor: Medium
Score: 6.9
Percentile: 96.51
CVSS v2
Risk Factor: Critical
Base Score: 10
Temporal Score: 7.4
Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C
CVSS Score Source: CVE-2026-82717
CVSS v3
Risk Factor: Critical
Base Score: 9.8
Temporal Score: 8.5
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C
CVSS v4
Risk Factor: Critical
Base Score: 9.5
Threat Score: 8.4
Threat Vector: CVSS:4.0/E:U
Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
Vulnerability Information
CPE: cpe:/o:amazon:linux:2, p-cpe:/a:amazon:linux:python2-unbound, p-cpe:/a:amazon:linux:python3-unbound, p-cpe:/a:amazon:linux:unbound-anchor, p-cpe:/a:amazon:linux:unbound-debuginfo, p-cpe:/a:amazon:linux:unbound-devel, p-cpe:/a:amazon:linux:unbound-libs, p-cpe:/a:amazon:linux:unbound-utils, p-cpe:/a:amazon:linux:unbound
Required KB Items: Host/local_checks_enabled, Host/AmazonLinux/release, Host/AmazonLinux/rpm-list
Exploit Ease: No known exploits are available
Patch Publication Date: 9/28/2026
Vulnerability Publication Date: 9/16/2026
Reference Information
CVE: CVE-2026-80225, CVE-2026-81634, CVE-2026-82717, CVE-2026-85501