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F5 Networks BIG-IP : NLnet Labs Unbound vulnerability (K000163001)
medium Nessus Plugin ID 339151
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Synopsis
The remote device is missing a vendor-supplied security patch.Description
The version of F5 Networks BIG-IP installed on the remote host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the K000163001 advisory.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)
Tenable has extracted the preceding description block directly from the F5 Networks BIG-IP security advisory.
Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.
Solution
The vendor has acknowledged the vulnerability, but no solution has been provided.Refer to the vendor for remediation guidance.
See Also
Plugin Details
Severity: Medium
ID: 339151
File Name: f5_bigip_SOL000163001.nasl
Version: 1.1
Type: Local
Published: 8/24/2026
Updated: 8/24/2026
Configuration: Enable paranoid mode
Supported Sensors: Nessus
Risk Information
VPR
Risk Factor: Low
Score: 1.2
Percentile: 0.01
CVSS v2
Risk Factor: Medium
Base Score: 5
Temporal Score: 3.7
Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:P
CVSS Score Source: CVE-2026-42923
CVSS v3
Risk Factor: Medium
Base Score: 5.3
Temporal Score: 4.6
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C
CVSS v4
Risk Factor: Medium
Base Score: 6.9
Threat Score: 2.7
Threat Vector: CVSS:4.0/E:U
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Vulnerability Information
CPE: cpe:/a:f5:big-ip_domain_name_system, cpe:/a:f5:big-ip_global_traffic_manager, cpe:/h:f5:big-ip
Required KB Items: Host/local_checks_enabled, Settings/ParanoidReport, Host/BIG-IP/hotfix, Host/BIG-IP/modules, Host/BIG-IP/version
Exploit Ease: No known exploits are available
Vulnerability Publication Date: 5/20/2026
Reference Information
CVE: CVE-2026-42923