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CVE-2026-33278

Nlnetlabs Unbound remote code execution

9.8 CRITICALEPSS 1.13%
  1. Published20 May 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Nlnetlabs Unbound≥ 1.19.1 < 1.25.1

Remediation

Fixed in
Nlnetlabs Unbound≥ 1.25.1

References

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Frequently asked

Is CVE-2026-33278 being actively exploited?

CVE-2026-33278 is not in the CISA KEV catalog. Its EPSS exploit probability is 1.13%.

How severe is CVE-2026-33278?

CVE-2026-33278 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 1.13% probability of exploitation.

Which products are affected by CVE-2026-33278?

Affected products include Nlnetlabs Unbound.

How do I fix CVE-2026-33278?

Upgrade affected software to a fixed version, for example Nlnetlabs Unbound 1.25.1 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.