CVE-2026-42959

Memory Safety in Nlnetlabs Unbound ≤ 1.25.1

Memory Safety

Published

20 May 2026

Modified

24 July 2026

Patch / advisory

View advisory

CVSS Score v4 8.7

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Raw vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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:X/V:X/RE:X/U:Red

EPSS Score 0.0078 53th percentile

Risk Priority 46 floored blend · peak EPSS

Summary

CVE-2026-42959 is a high-severity Access of Uninitialized Pointer (CWE-824) vulnerability in Nlnetlabs Unbound. Its CVSS base score is 8.7 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 47% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.

EU & UK References

🇪🇺 ENISA EUVD: EUVD-2026-31084

Vulnerability Data

NLnet Labs Unbound up to and including version 1.25.0 has a denial of service vulnerability in the DNSSEC validator that can lead to a crash given malicious upstream replies. When Unbound constructs chase-reply messages for validation, the code uses the…

wrong counter to calculate write offsets for ADDITIONAL section rrsets. DNAME duplication could increase the ANSWER section count and authority filtering could decrease the AUTHORITY section count and create an uninitialized array slot. Combining these two, the validator later dereferences this uninitialized pointer, causing an immediate process crash. An adversary controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue records. Unbound 1.25.1 contains a patch with a fix to use the proper counters to calculate the write offsets.

CWE(s): CWE-824

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 →

T1211 Exploitation for Stealth Stealth

Adversaries may exploit vulnerabilities to evade detection by hiding activity, suppressing logging, or operating within trusted or unmonitored components.

attack.mitre.org →

T1212 Exploitation for Credential Access Credential Access

Adversaries may exploit software vulnerabilities in an attempt to collect credentials.

attack.mitre.org →

Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-42944Same product: Nlnetlabs Unbound

CVE-2026-40691Same product: Nlnetlabs Unbound

CVE-2026-32792Same product: Nlnetlabs Unbound

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-2026-32665Same product: Nlnetlabs Unbound

Affected Assets

nlnetlabs

unbound

≤ 1.25.1

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation can discover uninitialized pointer accesses through static analysis, dynamic testing, or fuzzing before deployment.

SA-15 Development Process, Standards, and Tools partial match

Requiring documented development processes and tools enables use of analyzers or coding standards that identify uninitialized pointer defects.

SA-8 Security and Privacy Engineering Principles partial match

Security engineering principles can mandate memory-safety practices and language choices that structurally avoid uninitialized pointer use.

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.PS-06 mostly match

prevents

Secure SDLC practices directly prevent uninitialized pointer bugs via coding standards, analysis, and reviews, but eliminating this single weakness only partially fulfills the broader control.

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 uninitialized pointer usage before release.

A.8.25 Secure development life cycle partial match

prevents

Secure development life cycle mandates practices that reduce uninitialized pointer defects.

A.8.26 Application security requirements partial match

degrades

Application security requirements can specify pointer initialization rules.

A.8.27 Secure system architecture and engineering principles partial match

degrades

Secure architecture principles discourage unsafe pointer handling.