Cyber Resilience

CVE-2026-42955

Nlnetlabs Unbound 1.16.2 – 1.25.2

Published
22 July 2026
Modified
24 July 2026
Patch / advisory
View advisory
CVSS Score v3.1 3.7
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
EPSS Score 0.0020 11th percentile
Risk Priority 32 floored blend · peak EPSS

Summary

CVE-2026-42955 is a low-severity Operation on a Resource after Expiration or Release (CWE-672) vulnerability in Nlnetlabs Unbound. Its CVSS base score is 3.7 (Low).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 11th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and IA-5 (Authenticator Management) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

In NLnet Labs Unbound 1.16.2 up to and including 1.25.1, a similar vulnerability as with CVE-2026-40622 in the 'ghost domain names' family of attacks was found in Unbound that could extend the ghost domain window by up to one cached…

more

TTL configured value for A/AAAA glue records. Similar to other 'ghost domain names' attacks, an adversary needs to control a (ghost) zone and be able to query a vulnerable Unbound. A single client A/AAAA query can cause Unbound to overwrite the cached expired parent-side glue rrset and essentially extend the ghost domain window by up to one cached TTL configured value ('cache-max-ttl'). In configurations where 'harden-referral-path: yes' is used (non-default configuration), no client query is required since Unbound implicitly performs that query. This is a variant of CVE-2026-40622 which only addressed the NS query.

CWE(s)
CWE-672

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-33278Same product: Nlnetlabs Unbound
CVE-2026-52863Same product: Nlnetlabs Unbound
CVE-2026-44687Same product: Nlnetlabs Unbound
CVE-2026-55991Same product: Nlnetlabs Unbound
CVE-2026-42534Same product: Nlnetlabs Unbound
CVE-2026-50046Same product: Nlnetlabs Unbound
CVE-2026-55973Same product: Nlnetlabs Unbound
CVE-2026-32665Same product: Nlnetlabs Unbound
CVE-2026-32792Same product: Nlnetlabs Unbound
CVE-2026-42944Same product: Nlnetlabs Unbound

Affected Assets

nlnetlabs
unbound
1.16.2 — 1.25.2

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 1 hardening rule · 1 OS baseline
Validate
Prove the fix (OWASP ASVS)

—

Mitigating Controls (NIST 800-53 r5) AI

AC-3 Access Enforcement good match

Access enforcement applies current authorizations to every request, directly blocking operations once a resource has been revoked or released.

IA-5 Authenticator Management good match

Authenticator management mandates revocation and replacement procedures that render expired credentials unusable.

AC-2 Account Management partial match

Account lifecycle management includes explicit revocation and disabling steps that stop subsequent operations on released accounts or identifiers.

IA-4 Identifier Management partial match

Identifier management requires deallocation and reuse controls that prevent continued use of released identifiers.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-05 mostly match
prevents

Enforcing managed authorizations and revocations directly prevents post-release operations on credentials or entitlements.

PR.PS-06 mostly match
prevents

Secure development practices eliminate the root coding flaw that permits use-after-release.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect use-after-release but does not prevent it at runtime.

A.8.10 Information deletion partial match
degrades

Enforces timely deletion of resources so they cannot be used after release.

A.8.28 Secure coding partial match
prevents

Secure-coding rules require checks that prevent operations on freed or expired objects.

A.8.32 Change management partial match
prevents

Change-management processes can introduce or remove resource-lifetime controls.

References