dbcve.org
UnboundApplication · Nlnetlabs

CVE-2026-44390

MEDIUM · 5.3 CVSS v3.1 Published 2026-05-20
Fix available
A fix is available. Upgrade to 1.25.1 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability when handling replies with very large RRsets that Unbound needs to perform name compression for. Malicious upstream responses with very large RRsets with records that don't share a suffix above the root can cause Unbound to spend a considerable time applying name compression to downstream replies. This can lead to degraded performance and eventually denial of service in well orchestrated attacks. An adversary can exploit the vulnerability by querying Unbound for the specially crafted contents of a malicious zone with very large RRsets. Before Unbound replies to the query it will try to apply name compression which was an unbounded operation that could lock the CPU until the whole packet was complete. A compression limit was introduced in 1.21.1 for this but it didn't account for the case where records would not share any suffix above the root. That causes Unbound to go in a different code path because of the compression tree lookup failure and eventually not increment the compression counter for those operations. Unbound 1.25.1 contains a patch with a fix that increments the compression counter regardless of the compression tree lookup. This is a complement fix to CVE-2024-8508.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Unbound up to 1.25.0 contains an unbounded name compression vulnerability when processing DNS replies with very large RRsets where records don't share a suffix above the root. The compression counter introduced in 1.21.1 is not incremented in this specific code path due to compression tree lookup failure, causing unbounded CPU consumption that leads to degraded performance or denial of service. This is a complement fix to CVE-2024-8508.

MitigationUpgrade Unbound to version 1.25.1 or later, which contains the fix that increments the compression counter regardless of compression tree lookup results.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
UnboundApplication
Affected:< 1.25.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check if Unbound DNS resolver is installed
    Run 'unbound -h' or 'which unbound' to locate the Unbound binary
    Affected if The command fails or unbound is not found - Unbound is not present
  2. Determine the installed Unbound version
    Run 'unbound -h 2>&1 | head -1' or 'unbound -V' to display version information. Compare the version number to the affected range (< 1.25.1)
    Affected if Version shown is 1.25.0 or earlier (any version below 1.25.1)
  3. Verify the Unbound service is actively running
    Run 'systemctl status unbound' or 'service unbound status' depending on your init system
    Affected if Service is running - the vulnerable code path is active when Unbound processes DNS queries and upstream responses
  4. Confirm DNS resolver functionality is enabled
    Check the configuration file (typically /etc/unbound/unbound.conf) for 'interface:' directives and ensure local DNS service is bound to an address
    Affected if Unbound is configured to listen on network interfaces and resolve queries - the compression vulnerability applies to any upstream response processing

A user is affected if Unbound is installed and running with any version below 1.25.1, as the name compression flaw triggers during normal DNS response processing from upstream servers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 1.25.1 or later
Fixed in 1.25.1
Interim mitigation

Upgrade Unbound to version 1.25.1 or later, which contains the fix that increments the compression counter regardless of compression tree lookup results.

Recommended fix High confidence

1.25.1

  1. Check current Unbound version using 'unbound -V' or 'unbound-control version'
  2. Stop the Unbound service using 'systemctl stop unbound' or the appropriate command for your system
  3. Upgrade Unbound to version 1.25.1 using your system's package manager (e.g., 'apt-get install unbound=1.25.1' or 'yum install unbound-1.25.1')
  4. Verify the upgrade was successful by checking the installed version
  5. Restart the Unbound service using 'systemctl start unbound' or the appropriate command

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Unbound Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing4.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,540
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,464.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-44390 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data