Detections
Analytics
CentOS Linux 7 [TuxCare] Security Update: unbound / unbound-devel / unbound-libs / unbound-python Multiple Vulnerabilities (CENTOS7:CLSA-2026:1792811393)
high Nessus Plugin ID 372098
Synopsis
The CentOS Linux host is missing one or more security updates.Description
The CentOS Linux 7 host has packages installed that are affected by multiple vulnerabilities as referenced in the TuxCare CENTOS7:CLSA-2026:1792811393 advisory.- In NLnet Labs Unbound up to and including version 1.26.1, an observable cache-level side-channel can be exposed with 'unwanted-reply-threshold > 0' configurations (not a default configuration). If a response- like UDP datagram reaches the upstream source port currently used by a recursive query, but its TXID does not match any pending query, Unbound counts the packet as an unwanted reply. When the accumulated count reaches the configured threshold, Unbound clears the worker's RRset cache and message cache. This cache clear action does not destroy the current upstream UDP pending query. Therefore, an external observer can distinguish whether a candidate port matches the current upstream source port by checking whether an existing cached item has been cleared. This is a cache side-channel vulnerability that can be used to probe the upstream source port. Although the attack is not feasible on default configurations and the suggested value (10 million) makes it an ureliable attack on a public resolver, in scenarios where the attacker can keep a concurrent query window alive, the attacker can first filter the source port and then perform birthday-style guessing against the TXID, making cache poisoning a feasible attack path.
(CVE-2026-109125)
- When NLnet Labs Unbound 1.0.1 up to and including version 1.26.1 is configured with both a root trust anchor and an additional 'trust-anchor:' for an island-of-security zone whose parent is provably insecure under the root chain, a malicious actor with a forged NSEC reply with the SOA bit cleared can trick Unbound to treat the configured trust island as insecure. This happens because the DNSSEC validator in Unbound accepts and caches the NSEC insecure response bypassing the RRSIG validation that the validator was supposed to do. The acceptance of the NSEC record at the trust anchor apex was allowed due to and old fix for type DS and NSEC queries from clients when trust anchor for that name existed. (CVE-2026-35501)
- 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)
- When NLnet Labs Unbound up to and including version 1.26.1 is configured with both a root trust anchor and an additional 'trust-anchor:' for an island-of-security zone whose parent is provably insecure under the root chain, a malicious actor who can deliver one forged NXDOMAIN response for a name inside the island, with the NSEC/SOA RRSIG 'SignerName' set to the insecure parent, tricks Unbound's validator to use the root trust anchor instead, and consecutively the insecure parent, thus causing that record to be treated as insecure and denying existence for records in the trust island. (CVE-2026-50106)
- NLnet Labs Unbound up to and including version 1.26.1 limits compression-pointer traversal for each individual domain-name operation but has no aggregate inbound decompression-work budget. Many chained compression pointers in a message results in a lot of CPU usage following them. A malicious actor with recursive-query access and control of an ordinarily delegated authority that serves specially crafted replies can exploit the vulnerability and degrade Unbound's general performance. (CVE-2026-96405)
Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.
Solution
Update the affected packages based on the guidance in TuxCare advisory CENTOS7:CLSA-2026:1792811393.See Also
Plugin Details
Severity: High
ID: 372098
File Name: tuxcare_centos_7_CLSA-2026-1792811393.nasl
Version: 1.1
Type: Local
Agent: unix
Family: CentOS Local Security Checks
Published: 10/26/2026
Updated: 10/26/2026
Supported Sensors: Continuous Assessment, Nessus Agent, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus
Risk Information
VPR
Risk Factor: Low
Score: 3.5
Percentile: 51.51
Vendor
Vendor Severity: Important
CVSS v2
Risk Factor: High
Base Score: 7.8
Temporal Score: 5.8
Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:C/A:N
CVSS Score Source: CVE-2026-40622
CVSS v3
Risk Factor: High
Base Score: 7.5
Temporal Score: 6.5
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C
CVSS v4
Risk Factor: High
Base Score: 8.7
Threat Score: 6.6
Threat Vector: CVSS:4.0/E:U
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Vulnerability Information
Required KB Items: Host/OS/extended-third-party, Host/local_checks_enabled, Host/CentOS/release, Host/CentOS/rpm-list
Exploit Ease: No known exploits are available
Patch Publication Date: 10/24/2026
Vulnerability Publication Date: 5/20/2026
Reference Information
CVE: CVE-2025-5994, CVE-2026-109125, CVE-2026-35501, CVE-2026-40622, CVE-2026-50106, CVE-2026-96405
CLSA: 2026:1792811393