How severe is CVE-2026-33278?

CVE-2026-33278 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-33278 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (66th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33278?

CVE-2026-33278 affects Nlnetlabs Unbound. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33278?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-33278 have an EU (EUVD) identifier?

Yes. CVE-2026-33278 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-31075.

When was CVE-2026-33278 published?

CVE-2026-33278 was published on 2026-05-20 and last updated on 2026-06-30.

CVE-2026-33278

CVE-2026-33278 is a critical-severity vulnerability in Nlnetlabs Unbound with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-416.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v4: 9.1
EPSS exploit prediction: 1% (66th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-31075
Weakness: CWE-416
Affected product: Nlnetlabs Unbound
Published: 2026-05-20
Last modified: 2026-06-30

Description

NLnet Labs Unbound 1.19.1 up to and including version 1.25.0 has a vulnerability in the DNSSEC validator that enables denial of service and possible remote code execution as a result of deep copying a data structure and erroneously overwriting a destination pointer. An adversary can exploit the vulnerability by controlling a malicious signed zone and querying a vulnerable Unbound. When DS sub-queries need to suspend validation due to NSEC3 computational budget exhaustion (introduced in Unbound 1.19.1), Unbound deep-copies response messages to preserve them across memory region teardown. A struct-assignment bug overwrites the destination's pointer with the source's pointer. After the sub-query region is freed, the resumed validator dereferences this dangling pointer, triggering a crash or potentially enabling arbitrary code execution. Unbound 1.25.1 contains a patch with a fix to preserve the correct pointer when deep copying the data structure.

Frequently asked questions

What is CVE-2026-33278?: NLnet Labs Unbound 1.19.1 up to and including version 1.25.0 has a vulnerability in the DNSSEC validator that enables denial of service and possible remote code execution as a result of deep copying a data structure and erroneously overwriting a destination pointer. An adversary can exploit the vulnerability by controlling a malicious signed zone and querying a vulnerable Unbound. When DS sub-queries need to suspend validation due to NSEC3 computational budget exhaustion (introduced in Unbound 1.19.1), Unbound deep-copies response messages to preserve them across memory region teardown. A struct-assignment bug overwrites the destination's pointer with the source's pointer. After the sub-query region is freed, the resumed validator dereferences this dangling pointer, triggering a crash or potentially enabling arbitrary code execution. Unbound 1.25.1 contains a patch with a fix to preserve the correct pointer when deep copying the data structure.
How severe is CVE-2026-33278?: CVE-2026-33278 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-33278 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (66th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33278?: CVE-2026-33278 affects Nlnetlabs Unbound. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33278?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-33278 have an EU (EUVD) identifier?: Yes. CVE-2026-33278 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-31075.
When was CVE-2026-33278 published?: CVE-2026-33278 was published on 2026-05-20 and last updated on 2026-06-30.

References

Affected products (1)

cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*

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