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CentOS Linux 7 [TuxCare] Security Update: unbound / unbound-devel / unbound-libs / unbound-python Multiple Vulnerabilities (CENTOS7:CLSA-2026:1791327169)
critical Nessus Plugin ID 364644
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-2026:1791327169 advisory.- 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 the DNSSEC validator that enables denial of service and possible remote code execution as a result of digesting DNSKEYs. A DNSKEY with an owner compression pointer to its own RDATA can overflow the digest buffer. Remote code execution is possible through attacker controlled data. An adversary can exploit the vulnerability by controlling a malicious zone and querying a vulnerable Unbound. (CVE-2026-81642)
- 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)
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-2026:1791327169.See Also
Plugin Details
Severity: Critical
ID: 364644
File Name: tuxcare_centos_7_CLSA-2026-1791327169.nasl
Version: 1.1
Type: Local
Agent: unix
Family: CentOS Local Security Checks
Published: 10/12/2026
Updated: 10/12/2026
Supported Sensors: Nessus Agent, Continuous Assessment, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus
Risk Information
VPR
Risk Factor: High
Score: 7.7
Percentile: 98.93
Vendor
Vendor Severity: Critical
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: 10
Threat Score: 9.1
Threat Vector: CVSS:4.0/E:U
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
CVSS Score Source: CVE-2026-81642
Vulnerability Information
Required KB Items: Host/local_checks_enabled, Host/CentOS/release, Host/CentOS/rpm-list, Host/OS/extended-third-party
Exploit Ease: No known exploits are available
Patch Publication Date: 10/6/2026
Vulnerability Publication Date: 9/16/2026
Reference Information
CVE: CVE-2026-81634, CVE-2026-81642, CVE-2026-82717, CVE-2026-85501
CLSA: 2026:1791327169