CVE-2025-5994Network attack vector

DNS cache poisoning via raced non-ECS replies

Published Jul 16, 2025 · Updated Nov 3, 2025

DNS cache poisoning in NLnet Labs Unbound 1.6.2 through 1.23.0 allows remote attackers to cache forged non-ECS replies. With ECS query segregation enabled, the resolver accepts a raced non-ECS reply whose guessed transaction ID matches an outstanding ECS query instead of preserving query aggregation. Exploitation requires an ECS-enabled build, outbound ECS configuration, attacker-triggered segregated queries, and a forged reply that wins the race; successful poisoning redirects later DNS resolutions.

CVSS severity8.7
High
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

DNS cache poisoning in NLnet Labs Unbound 1.6.2 through 1.23.0 allows remote attackers to cache forged non-ECS replies. With ECS query segregation enabled, the resolver accepts a raced non-ECS reply whose guessed transaction ID matches an outstanding ECS query instead of preserving query aggregation. Exploitation requires an ECS-enabled build, outbound ECS configuration, attacker-triggered segregated queries, and a forged reply that wins the race; successful poisoning redirects later DNS resolutions.

The record

CVE
CVE-2025-5994
Published
Jul 16, 2025
Updated
Nov 3, 2025
Vendor
NLnet Labs
Product
Unbound
Classifications
CWE-349, CAPEC-142, T1565.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 16, 2025CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.6.2 <1.23.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NLnet Labs · Unboundversion=1.6.2 <1.23.0

Published CVSS scores

8.7National Vulnerability DatabaseCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:U/V:C/RE:X/U:X

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-349Acceptance of Extraneous Untrusted Data With Trusted Data
CAPEC-142DNS Cache Poisoning
T1565.002Transmitted Data Manipulation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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