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NVD / CVE Program· CNA NLnet Labs

CVE-2026-44608: Use after free and crash under special conditions in RPZ code

MediumCVSS 4.6 · v4.0—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 18/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.25% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
  • Fixed version: NLnet Labs Unbound 1.25.1; azl3 unbound 1.19.1-5 on Azure Linux 3.0 1.25.1-1.

Low priority for now. Upgrade to NLnet Labs Unbound 1.25.1; azl3 unbound 1.19.1-5 on Azure Linux 3.0 1.25.1-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a locking inconsistency vulnerability that when certain conditions are met (multi-threaded, RPZ XFR reload, RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers) it could result in heap use-after-free and eventual crash. An adversary can exploit the vulnerability if conditions are first met on a vulnerable Unbound, i.e., multi-threaded, an RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers and an ongoing XFR for that RPZ zone. Local RPZ files do not trigger the vulnerability. If the timing is right and an XFR happens at the same time another thread needs to read that RPZ zone, the reader may not hold the lock long enough and the thread applying the XFR may free objects that the reader is about to walk causing the use-after-free. Unbound 1.25.1 contains a patch with a fix to the locking code.

Published
May 20, 2026
Updated
Jul 24, 2026
EPSS
0.2% · 17th percentile

Report tools

JSON

Action score

18

Monitor

Low priority for now.

CVSS
18 / 40 · 4.6 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · NLnet Labs
4.6
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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Follow CVE-2026-44608

When you'll hear from us

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  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
nlnetlabsunbound

Versions reported by the vendor

Affected version ranges reported by the assigning authority (NLnet Labs). Independent of NVD's CPE analysis and usually ahead of it.

  • NLnet Labs Unbound

    • 1.14.0 and later · before 1.25.1affected · semver

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • nlnetlabs unbound1.14.0 and later · before 1.25.1

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Alpine:v3.22unboundfrom 1.14.0 · before 1.25.2-r01.25.2-r0
Alpine:v3.24unboundfrom 1.14.0 · before 1.25.1-r01.25.1-r0
Debian:12unboundfrom 0—
Debian:13unboundbefore 1.22.0-2+deb13u31.22.0-2+deb13u3
Debian:14unboundbefore 1.25.1-11.25.1-1
openSUSE:Leap 16.0unboundbefore 1.24.1-160000.2.11.24.1-160000.2.1
openSUSE:Tumbleweedunboundbefore 1.25.1-1.11.25.1-1.1
Red Hat:hummingbird:1python3-unboundbefore 0:1.25.1-0.1.hum10:1.25.1-0.1.hum1
Red Hat:hummingbird:1unboundbefore 0:1.25.1-0.1.hum10:1.25.1-0.1.hum1
Red Hat:hummingbird:1unbound-anchorbefore 0:1.25.1-0.1.hum10:1.25.1-0.1.hum1
Red Hat:hummingbird:1unbound-develbefore 0:1.25.1-0.1.hum10:1.25.1-0.1.hum1
Red Hat:hummingbird:1unbound-dracutbefore 0:1.25.1-0.1.hum10:1.25.1-0.1.hum1
Red Hat:hummingbird:1unbound-libsbefore 0:1.25.1-0.1.hum10:1.25.1-0.1.hum1
Red Hat:hummingbird:1unbound-muninbefore 0:1.25.1-0.1.hum10:1.25.1-0.1.hum1
Red Hat:hummingbird:1unbound-utilsbefore 0:1.25.1-0.1.hum10:1.25.1-0.1.hum1
SUSE:Linux Enterprise Micro 5.5unboundbefore 1.20.0-150100.10.25.11.20.0-150100.10.25.1
SUSE:Linux Enterprise Server 16.0unboundbefore 1.24.1-160000.2.11.24.1-160000.2.1

Same product

nlnetlabs: all records

Other highest-scoring records for the same primary product.

  • CVE-2019-25042Unbound before 1.9.5 allows an out-of-bounds write via a compressed name in rdata_copy.
    40Plan
  • CVE-2019-25039Unbound before 1.9.5 allows an integer overflow in a size calculation in respip/respip.c.
    40Plan
  • CVE-2019-25038Unbound before 1.9.5 allows an integer overflow in a size calculation in dnscrypt/dnscrypt.c.
    40Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-42960May 20, 2026 · Possible cache poisoning via promiscuous records for the authority section
    22Monitor
  • ← EarlierCVE-2026-44390May 20, 2026 · Unbounded name compression in certain cases causes degradation of service
    27Monitor
  • Later →CVE-2026-32665Jul 22, 2026 · Remote DNS-over-QUIC denial of service due to `quic-size` budget bypass
    30Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
NLnet Labs Unbound1.25.1Vendor (CNA)
azl3 unbound 1.19.1-5 on Azure Linux 3.01.25.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
alpine:unbound1.25.2-r0 · Alpine:v3.22Package registry (OSV)
debian:unbound1.22.0-2+deb13u3 · Debian:13Package registry (OSV)
opensuse:unbound1.25.1-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:python3-unbound0:1.25.1-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound0:1.25.1-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-anchor0:1.25.1-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-devel0:1.25.1-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-dracut0:1.25.1-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-libs0:1.25.1-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-munin0:1.25.1-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-utils0:1.25.1-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
suse:unbound1.24.1-160000.2.1 · SUSE:Linux Enterprise Server 16.0Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Not on record for this CVE: EPSS history · patch commit or PR link · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-413 · Improper Resource Locking

CVSS vector

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/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:Amber

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records