Detections
Analytics

Echo: unbound: security update to 1.25.2

high Tenable Cloud Security Plugin ID 458039

Description

There are packages installed that are affected by a vulnerability referenced in the following CVE:

 - 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)

Solution

Update the unbound library and its related packages to version 1.25.2 or later.

See Also

https://advisory.echohq.com/cve/CVE-2026-50252

Plugin Details

Severity: High

ID: 458039

Version: Revision 1.2

Type: Local

Published: 10/2/2026

Updated: 10/5/2026

Supported Sensors: Tenable Cloud Security, Tenable Self-Hosted Container Security

Risk Information

VPR

Risk Factor: Medium

Score: 6.8

Percentile: 96.54

CVSS v2

Risk Factor: High

Base Score: 7.8

Temporal Score: 5.8

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

CVSS Score Source: CVE-2026-50252

CVSS v3

Risk Factor: Critical

Base Score: 9.3

Temporal Score: 8.1

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:O/RC:C

CVSS v4

Risk Factor: High

Base Score: 7.1

Threat Score: 5.7

Threat Vector: CVSS:4.0/E:P

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

Exploit Ease: No known exploits are available

Patch Publication Date: 7/23/2026

Vulnerability Publication Date: 7/22/2026

Reference Information

CVE: CVE-2026-50252