Crash during DNSSEC validation of malicious content (NLnet Labs Unbound)

CVE-2026-42959

HIGH 8.7

At a glance

Source: NVD
EPSS: EPSS 0.81 % · percentile 57 (2026-10-31)
State: PUBLISHED
Published: 2026-05-20 09:20 UTC
Updated: 2026-09-01 12:05 UTC
Assigner: NLnet Labs
NVD status: Modified

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Description

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.

Weaknesses (CWE)

CWE-824 — Access of Uninitialized Pointer

References

Scores

Version	Score	Vector	Scored by
CVSS 4.0	HIGH 8.7	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/U:Red	NLnet Labs
CVSS 3.1	HIGH 7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	redhat-SADP
CVSS 4.0	HIGH 8.7	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	NVD · sep@nlnetlabs.nl (Secondary)
CVSS 3.1	HIGH 7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	NVD · nvd@nist.gov (Primary)
CVSS 3.1	HIGH 7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	NVD · 0b0ca135-0b70-47e7-9f44-1890c2a1c46c (Secondary)

European references

ENISA EUVD · EUVD-2026-31084
GCVE · GCVE-0-2026-42959

CERT-FR advisories

CERTFR-2026-AVI-1111 — Multiples vulnérabilités dans les produits F5 · cert.ssi.gouv.fr
CERTFR-2026-AVI-0986 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr

Affected configurations (NVD CPE)

cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:* < 1.25.1

Affected products

Product	Versions
NLnet Labs · Unbound	affected 0 < 1.25.1

Sources

Source	Licence
CVE List (CVEProject cvelistV5)	CVE Program Terms of Use
EPSS (FIRST.org)	FIRST — attribution requested
ENISA EUVD	ENISA — reproduction authorised, source acknowledged
CERT-FR (ANSSI)	Licence Ouverte / Etalab 2.0
NVD (NIST) via fkie-cad/nvd-json-data-feeds	Public domain — this product uses data from the NVD API but is not endorsed or certified by the NVD

⚠️ Crash during DNSSEC validation of malicious content (NLnet Labs Unbound)