Vulnary
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Critical· 9.1official fix available

CVE-2026-33278

Unbound, a DNS resolver, has a bug that can crash the service or let an attacker run code when it processes certain DNSSEC queries. The flaw occurs when Unbound copies data structures during validation, accidentally pointing to freed memory. A malicious zone can trigger this by sending specially crafted DNS responses.

publishedMay 20, 2026
last modifiedJul 24, 2026
sourcesNVD
severity · cvss
9.1
critical · how bad it is
exploitation · epss
1%
67th percentile · chance of exploitation in 30 days
(ai-assisted) A model wrote this summary from the official data, so double-check it against the source before you act on it. Read the official advisory →
auto-deletes from the system
counting…on Aug 24, 2026

An official fix is available, so this entry is kept for 30 days and then removed automatically.

01

Who is affected

NLnet Labs Unbound versions 1.19.1 through 1.25.0. System administrators who run Unbound as a DNS resolver are affected.

02

Real-world impact

An attacker could cause the Unbound service to crash, leading to denial of DNS resolution for users, or potentially execute arbitrary code on the host, compromising the entire system.

03

Why this severity

The CVSS score of 9.1 reflects that the vulnerability is exploitable over the network without authentication, requires no user interaction, and can lead to both denial of service and remote code execution. The high impact and lack of mitigations in the affected versions contribute to the critical rating.

04

What to do about it

official fix available
recommended steps
  1. 01Upgrade Unbound to version 1.25.1 or later.
  2. 02Restart the Unbound service to apply the update.

NVD-referenced vendor advisory

05

Timeline

  1. May 20, 2026 · May 20, 2026
    Published
    Disclosed and added to the National Vulnerability Database.
  2. Jul 24, 2026 · 12d ago
    Advisory updated
    The NVD record was last revised.
  3. Jul 25, 2026 · 10d ago
    Official fix available
    A vendor patch or mitigation now exists — see the remediation steps above.
06

How it’s attacked

Attack vectorNetwork (remote)
Attack complexityLow
Attack requirementsNone
Privileges requiredNone
User interactionNone needed
Confidentiality impactHigh
Integrity impactHigh
Availability impactHigh
07

References & advisories

NVD advisory ↗Search advisories ↗
(ai-assisted) A model wrote this summary from the official data, so double-check it against the source before you act on it. Read the official advisory →