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.
Affected products
nlnetlabs: unbound
References7
- www.nlnetlabs.nl/downloads/unbound/CVE-2026-33278.txt MitigationVendor Advisory
- access.redhat.com/errata/RHSA-2026:19752
- access.redhat.com/errata/RHSA-2026:23231
- access.redhat.com/errata/RHSA-2026:24369
- access.redhat.com/security/cve/CVE-2026-33278
- bugzilla.redhat.com/show_bug.cgi?id=2479808
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33278…
Metrics
- CVSS 3.1
-
9.8
CRITICAL
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H - CVSS 4.0
-
9.1
CRITICAL
Score source: CNA
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:U/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 — exploit probability
- 1% percentile: 73 · as of 14 November 2026
- CWE
- CWE-416CWE-672
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