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NVD / CVE Program· CNA NLnet Labs

CVE-2026-50243: 'response-ip'/'rpz' can rewrite BOGUS answers instead of returning SERVFAIL

Noroxi assessment

Priority: Monitor (action score 25/100)

  • 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: 0.10% (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 1.25.2; azl3 unbound 1.25.1-1 on Azure Linux 3.0 1.25.2-1.

Low priority for now. Upgrade to NLnet Labs Unbound 1.25.2; azl3 unbound 1.25.1-1 on Azure Linux 3.0 1.25.2-1 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

In NLnet Labs Unbound 1.6.2 up to and including 1.25.1, when Unbound is configured with the 'respip' module in front of the validator together with a 'response-ip' redirect rule or an RPZ file with an RPZ-IP trigger, the rewriting handler does not check the security status of the upstream answer and can instead rewrite a BOGUS A/AAAA answer to point to an operator's configured IP. If the validator finds an expired or otherwise invalid RRSIG on an answer whose A record falls within a 'response-ip'/RPZ configuration, the answer is still rewritten and given a hard coded security level of INSECURE. This results in the client receiving an INSECURE NOERROR reply rewritten by the operator's configured IP. A malicious actor can exploit the possible poisonous effect by spoofing a BOGUS A/AAAA answer that falls inside the operator's configured subnet rewrites. Such DNSSEC protected answers are then insecurely redirected to the operator's configured target.

MediumCVSS 6.3 · v4.0—No exploit Fix available
Published
Jul 22, 2026
Updated
Oct 24, 2026
EPSS
0.1% · 1th percentile

Report tools

JSON

Action score

25

Monitor

Low priority for now.

CVSS
25 / 40 · 6.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · NLnet Labs
6.3
NVD has not scored this yet; the score shown is the CNA’s.

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

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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When you'll hear from us

  • when it enters CISA KEV
  • 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

Affected versions

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

  • nlnetlabs unbound1.6.2 and later · before 1.25.2

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

    • 1.6.2 and later · before 1.25.2affected · semver

Package-level exposure

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

EcosystemPackageAffected rangeFix
Alpine:v3.22unboundfrom 1.6.2 · before 1.25.2-r01.25.2-r0
Debian:12unboundfrom 0—
Debian:13unboundbefore 1.26.1-0+deb13u11.26.1-0+deb13u1
Debian:14unboundbefore 1.25.2-11.25.2-1
openSUSE:Leap 16.0unboundbefore 1.25.2-160000.1.11.25.2-160000.1.1
openSUSE:Tumbleweedunboundbefore 1.25.2-1.11.25.2-1.1
Red Hat:hummingbird:1python3-unboundbefore 0:1.25.2-0.1.hum10:1.25.2-0.1.hum1
Red Hat:hummingbird:1unboundbefore 0:1.25.2-0.1.hum10:1.25.2-0.1.hum1
Red Hat:hummingbird:1unbound-anchorbefore 0:1.25.2-0.1.hum10:1.25.2-0.1.hum1
Red Hat:hummingbird:1unbound-develbefore 0:1.25.2-0.1.hum10:1.25.2-0.1.hum1
Red Hat:hummingbird:1unbound-dracutbefore 0:1.25.2-0.1.hum10:1.25.2-0.1.hum1
Red Hat:hummingbird:1unbound-libsbefore 0:1.25.2-0.1.hum10:1.25.2-0.1.hum1
Red Hat:hummingbird:1unbound-muninbefore 0:1.25.2-0.1.hum10:1.25.2-0.1.hum1
Red Hat:hummingbird:1unbound-utilsbefore 0:1.25.2-0.1.hum10:1.25.2-0.1.hum1
SUSE:Linux Enterprise Micro 5.5unboundbefore 1.25.2-150100.10.28.11.25.2-150100.10.28.1
SUSE:Linux Enterprise Module for Basesystem 15 SP7unboundbefore 1.25.2-150600.23.19.11.25.2-150600.23.19.1
SUSE:Linux Micro 6.0unboundbefore 1.25.2-1.11.25.2-1.1
SUSE:Linux Micro 6.1unboundbefore 1.25.2-slfo.1.1_1.11.25.2-slfo.1.1_1.1
SUSE:Linux Micro 6.2unboundbefore 1.25.2-160000.1.11.25.2-160000.1.1

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-2026-50045Jul 22, 2026 · 'max-global-quota' reset by DNSSEC validation restarts
    21Monitor
  • ← EarlierCVE-2026-50046Jul 22, 2026 · Possible heap use-after-free in an error path when a DoT forwarded query is jostled out
    23Monitor
  • Later →CVE-2026-50248Jul 22, 2026 · BOGUS configured primary hostname accepted for XFR in auth/rpz zones
    26Monitor

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 Unbound1.25.2Vendor (CNA)
azl3 unbound 1.25.1-1 on Azure Linux 3.01.25.2-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
alpine:unbound1.25.2-r0 · Alpine:v3.22Package registry (OSV)
debian:unbound1.26.1-0+deb13u1 · Debian:13Package registry (OSV)
opensuse:unbound1.25.2-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:python3-unbound0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-anchor0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-devel0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-dracut0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-libs0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-munin0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:unbound-utils0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
suse:unbound1.25.2-160000.1.1 · SUSE:Linux Micro 6.2Package 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.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

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

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

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-348 · Use of Less Trusted Source

CVSS vector

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N/E:X/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:X

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.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

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

All records