Possible arbitrary code execution during DNSSEC validation
Summary
| CVE | CVE-2026-33278 |
|---|---|
| State | PUBLISHED |
| Assigner | NLnet Labs |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-05-20 10:16:26 UTC |
| Updated | 2026-06-30 03:18:39 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 9.1 CRITICAL from [email protected]
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: 0.012720000 probability, percentile 0.663380000 (date 2026-07-04)
Problem Types: CWE-416 | CWE-672 | CWE-416 CWE-416: Use After Free | CWE-672 CWE-672: Operation on a Resource after Expiration or Release | CWE-416 Use After Free
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 9.1 | CRITICAL | 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/C... |
| 4.0 | CNA | CVSS | 9.1 | CRITICAL | 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/U... |
| 3.1 | [email protected] | Primary | 9.8 | CRITICAL | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| 3.1 | ADP | CVSS | 8.1 | HIGH | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H |
| 3.1 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | Secondary | 8.1 | HIGH | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H |
CVSS v4.0 Breakdown
Attack Vector
NetworkAttack Complexity
LowAttack Requirements
NonePrivileges Required
NoneUser Interaction
NoneConfidentiality
HighIntegrity
HighAvailability
HighSub Conf.
HighSub Integrity
HighSub Availability
HighCVSS: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
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
HighIntegrity
HighAvailability
HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD Known Affected Configurations (CPE 2.3)
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | NLnet Labs | Unbound | affected 1.19.1 1.25.1 semver | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux AppStream V. 10 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux AppStream V. 9 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux CodeReady Linux Builder V. 10 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux CodeReady Linux Builder V. 9 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Hardened Images | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 6 | Not specified | Not specified |
| ADP | Red Hat | Red Hat OpenShift Container Platform 4 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 7 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 8 | Not specified | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| access.redhat.com/errata/RHSA-2026:23231 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| bugzilla.redhat.com/show_bug.cgi | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | bugzilla.redhat.com | |
| security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33278.json | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | security.access.redhat.com | |
| access.redhat.com/errata/RHSA-2026:19752 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| access.redhat.com/security/cve/CVE-2026-33278 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| www.nlnetlabs.nl/downloads/unbound/CVE-2026-33278.txt | [email protected] | www.nlnetlabs.nl | Mitigation, Vendor Advisory |
| access.redhat.com/errata/RHSA-2026:24369 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Qifan Zhang (Palo Alto Networks) (en)
Additional Advisory Data
| Source | Time | Event |
|---|---|---|
| CNA | 2026-04-15T00:00:00.000Z | Issue reported by Qifan Zhang |
| CNA | 2026-04-29T00:00:00.000Z | NLnet Labs shares patch |
| CNA | 2026-04-29T00:00:00.000Z | Qifan Zhang verifies patch |
| CNA | 2026-05-20T00:00:00.000Z | Fixes released with version 1.25.1 |
| ADP | 2026-05-19T11:46:56.937Z | Reported to Red Hat. |
| ADP | 2026-05-20T11:33:59.504Z | Made public. |
Solutions
CNA: This issue is fixed starting with version 1.25.1
ADP: RHSA-2026:23231: Red Hat Enterprise Linux AppStream (v. 10), Red Hat Enterprise Linux CodeReady Linux Builder (v. 10)
ADP: RHSA-2026:24369: Red Hat Enterprise Linux AppStream (v. 9), Red Hat Enterprise Linux CodeReady Linux Builder (v. 9)
ADP: RHSA-2026:19752: Red Hat Hardened Images
There are currently no legacy QID mappings associated with this CVE.