Linux Distros Unpatched Vulnerability : CVE-2026-50252

high Nessus Plugin ID 329603

Synopsis

The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be patched.

Description

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

- In NLnet Labs Unbound 1.4.22 up to and including 1.25.1, UDP source port is randomized and intended to serve as a secret value that increases the entropy of DNS transactions. When resolver load balancing policies depend on the source port while their outcome is revealed this secrecy is undermined. The vulnerability arises when the load balancing policy is consistent with respect to the incoming source UDP port and IP address while heavily depending on the incoming source UDP port as a randomization source.
When the SO_REUSEPORT configuration option is enabled ('so-reuseport: yes') in Unbound (by default), it meets these conditions, making it vulnerable for DNS cache poisoning attacks. Upon startup, Unbound randomly partitions the available UDP source port space into disjoint subsets of (almost) equal size, assigning each subset to a specific worker thread. When an incoming DNS query is received, the kernel's SO_REUSEPORT load balancing mechanism deterministically assigns the query to a socket associated with a particular thread. All outgoing DNS queries generated during the resolution of that request use source ports selected exclusively from the port subset assigned to the corresponding thread. Since these port subsets are disjoint across threads, the source port observed in a resolver's outgoing query to an authoritative name server serves as a reliable indicator of the worker thread that processed the original client query. A malicious actor can acquire the mapping between incoming UDP source ports (for a given fixed source IP address) and Unbound worker threads and leverage it to conduct DNS cache poisoning attacks by effectively lowering the random port population per thread. (CVE-2026-50252)

Note that Nessus relies on the presence of the package as reported by the vendor.

Solution

There is no known solution at this time.

Plugin Details

Severity: High

ID: 329603

File Name: unpatched_CVE_2026_50252.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Misc.

Published: 7/25/2026

Updated: 7/25/2026

Supported Sensors: Agentless Assessment, Frictionless Assessment Agent, Frictionless Assessment AWS, Frictionless Assessment Azure, Nessus Agent, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.8

Percentile: 57.84

CVSS v2

Risk Factor: Medium

Base Score: 6.4

Temporal Score: 5.4

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:P/A:P

CVSS Score Source: CVE-2026-50252

CVSS v3

Risk Factor: Critical

Base Score: 9.3

Temporal Score: 8.5

Vector: CVSS:3.0/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:U/RC:C

CVSS v4

Risk Factor: High

Base Score: 7.1

Threat Score: 4.1

Threat Vector: CVSS:4.0/E:U

Vector: CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:H

Vulnerability Information

CPE: cpe:/o:canonical:ubuntu_linux:14.04:-:lts, cpe:/o:canonical:ubuntu_linux:16.04:-:lts, cpe:/o:canonical:ubuntu_linux:18.04:-:lts, cpe:/o:canonical:ubuntu_linux:20.04:-:lts, cpe:/o:canonical:ubuntu_linux:22.04:-:lts, cpe:/o:canonical:ubuntu_linux:24.04:-:lts, cpe:/o:canonical:ubuntu_linux:26.04:-:lts, cpe:/o:debian:debian_linux:11.0, cpe:/o:debian:debian_linux:12.0, cpe:/o:debian:debian_linux:13.0, cpe:/o:debian:debian_linux:14.0, p-cpe:/a:canonical:ubuntu_linux:unbound, p-cpe:/a:debian:debian_linux:unbound

Required KB Items: Host/cpu, Host/local_checks_enabled, global_settings/vendor_unpatched, Host/OS/identifier

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 7/22/2026

Reference Information

CVE: CVE-2026-50252

Detections

Analytics