CVE-2026-19538Network attack vector

Blocked DNS data disclosure via repeated persistent queries

Published Aug 26, 2026 · Updated Aug 26, 2026

Access-control bypass in NLnet Labs NSD 4.8.0 through 4.15.0 allows remote attackers to read blocked DNS data via TCP or TLS. On a persistent proxy-protocol connection, NSD enforces the BLOCKED ACL for the first DNS query but fails to preserve that denial for the second query. The proxy-protocol port must be configured and reachable, and the attacker must keep one connection open; the bypass permits queries that the zone ACL was intended to discard.

CVSS severity8.2
High
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Access-control bypass in NLnet Labs NSD 4.8.0 through 4.15.0 allows remote attackers to read blocked DNS data via TCP or TLS. On a persistent proxy-protocol connection, NSD enforces the BLOCKED ACL for the first DNS query but fails to preserve that denial for the second query. The proxy-protocol port must be configured and reachable, and the attacker must keep one connection open; the bypass permits queries that the zone ACL was intended to discard.

The record

CVE
CVE-2026-19538
Published
Aug 26, 2026
Updated
Aug 26, 2026
Vendor
NLnet Labs
Product
NSD
Classifications
CWE-672, CWE-290, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 26, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 26, 2026Record 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=4.8.0 <4.15.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NLnet Labs · NSDversion=4.8.0 <4.15.1

Published CVSS scores

8.2NLnet LabsCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-672Operation on a Resource after Expiration or Release
CWE-290Authentication Bypass by Spoofing
T1190Exploit Public-Facing Application

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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