Detections
Analytics

Echo: unbound: security update to 1.25.2

medium Tenable Cloud Security Plugin ID 460922

Description

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

 - In NLnet Labs Unbound up to and including version 1.25.1, when 'unwanted-reply-threshold' is enabled (set
 to any value greater than zero), glue records of 0.0.0.0/::0 can short-circuit Unbound, on systems that
 can direct such traffic, by issuing DNS queries and receiving seemingly unwanted replies since the remote
 IP does not match the original source IP of 0.0.0.0/::0. This behavior keeps on looping for the glue
 records and pushing the counter to the configured 'unwanted-reply-threshold' that triggers a defensive
 cache clear. A malicious actor who controls a delegation that returns in-bailiwick glue of 0.0.0.0/::0 can
 drive the counter to the limit of 'unwanted-reply-threshold' to the threshold and trigger a cache clean of
 the message and rrset caches; at will, indefinitely, without sending a single spoofed packet. The iterator
 uses the 0.0.0.0/::0 glue, and a system that can route this (e.g., Linux kernel routes the datagram over
 loopback), Unbound's own listener answers from 127.0.0.1. Because of the mismatch of 0.0.0.0 and
 127.0.0.1, in this example, Unbound accounts the reply as an unwanted (probably spoofed) answer. The
 counter resets to zero on every cache flush, so the attack loops forever. (CVE-2026-50251)

Solution

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

See Also

https://advisory.echohq.com/cve/CVE-2026-50251

Plugin Details

Severity: Medium

ID: 460922

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: 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-2026-50251

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

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-2026-50251