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NVD / CVE Program· CNA NLnet Labs

CVE-2025-5994: Cache poisoning via the ECS-enabled Rebirthday Attack

Noroxi assessment

Priority: Monitor (action score 34/100)

  • 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: 0.21% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: NLnet Labs Unbound 1.23.0.

Low priority for now. Upgrade to NLnet Labs Unbound 1.23.0 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

A multi-vendor cache poisoning vulnerability named 'Rebirthday Attack' has been discovered in caching resolvers that support EDNS Client Subnet (ECS). Unbound is also vulnerable when compiled with ECS support, i.e., '--enable-subnet', AND configured to send ECS information along with queries to upstream name servers, i.e., at least one of the 'send-client-subnet', 'client-subnet-zone' or 'client-subnet-always-forward' options is used. Resolvers supporting ECS need to segregate outgoing queries to accommodate for different outgoing ECS information. This re-opens up resolvers to a birthday paradox attack (Rebirthday Attack) that tries to match the DNS transaction ID in order to cache non-ECS poisonous replies.

HighCVSS 8.7 · v4.0—No exploit Fix available
Published
Jul 16, 2025
Updated
Jun 17, 2026
EPSS
0.2% · 12th percentile

Report tools

JSON

Action score

34

Monitor

Low priority for now.

CVSS
34 / 40 · 8.7 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · NLnet Labs
8.7
NVD has not scored this yet; the score shown is the CNA’s.

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

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

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2025-5994

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.

—

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 1.23.0affected · semver

Package-level exposure

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

EcosystemPackageAffected rangeFix
AlmaLinux:10python3-unboundbefore 1.20.0-12.el10_01.20.0-12.el10_0
AlmaLinux:10unboundbefore 1.20.0-12.el10_01.20.0-12.el10_0
AlmaLinux:10unbound-anchorbefore 1.20.0-12.el10_01.20.0-12.el10_0
AlmaLinux:10unbound-develbefore 1.20.0-12.el10_01.20.0-12.el10_0
AlmaLinux:10unbound-dracutbefore 1.20.0-12.el10_01.20.0-12.el10_0
AlmaLinux:10unbound-libsbefore 1.20.0-12.el10_01.20.0-12.el10_0
AlmaLinux:8python3-unboundbefore 1.16.2-5.9.el8_101.16.2-5.9.el8_10
AlmaLinux:8unboundbefore 1.16.2-5.9.el8_101.16.2-5.9.el8_10
AlmaLinux:8unbound-develbefore 1.16.2-5.9.el8_101.16.2-5.9.el8_10
AlmaLinux:8unbound-libsbefore 1.16.2-5.9.el8_101.16.2-5.9.el8_10
AlmaLinux:9python3-unboundbefore 1.16.2-19.el9_6.11.16.2-19.el9_6.1
AlmaLinux:9unboundbefore 1.16.2-19.el9_6.11.16.2-19.el9_6.1
AlmaLinux:9unbound-develbefore 1.16.2-19.el9_6.11.16.2-19.el9_6.1
AlmaLinux:9unbound-dracutbefore 1.16.2-19.el9_6.11.16.2-19.el9_6.1
AlmaLinux:9unbound-libsbefore 1.16.2-19.el9_6.11.16.2-19.el9_6.1
Alpine:v3.19unboundbefore 1.20.0-r21.20.0-r2
Alpine:v3.21unboundbefore 1.22.0-r11.22.0-r1
Alpine:v3.22unboundbefore 1.23.1-r01.23.1-r0
Debian:11unboundbefore 1.13.1-1+deb11u51.13.1-1+deb11u5
Debian:12unboundbefore 1.17.1-2+deb12u31.17.1-2+deb12u3
Debian:13unboundbefore 1.22.0-21.22.0-2
openSUSE:Tumbleweedunboundbefore 1.23.1-1.11.23.1-1.1
Red Hat:enterprise_linux:10.0python3-unboundbefore 0:1.20.0-12.el10_00:1.20.0-12.el10_0
Red Hat:enterprise_linux:10.0python3-unbound-debuginfobefore 0:1.20.0-12.el10_00:1.20.0-12.el10_0

+83

Same product

nlnet labs: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-97206DNS-over-QUIC (DoQ) path-migration can lead to use-after-free on multi-threaded deployments.
    30Monitor
  • CVE-2026-50106Possible insecure NXDOMAIN for non-existing records under a configured island trust anchor underneath an insecure parent.
    26Monitor
  • CVE-2026-14586Assertion in libngtcp2 when under pressure in high concurrency DNS-over-QUIC environments
    23Monitor

Published before and after this one in the same product

  • Later →CVE-2025-11411Oct 22, 2025 · Possible domain hijacking via promiscuous records in the authority section
    22Monitor
  • Later →CVE-2026-109125Oct 21, 2026 · Possible cache poisoning vulnerability via a cache side-channel exposed by 'unwanted-reply-threshold'
    21Monitor
  • Later →CVE-2026-35501Oct 21, 2026 · Bypass of a configured island trust anchor underneath an insecure parent from an atacker-controlled NSEC record.
    14Monitor

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 Unbound1.23.0Vendor (CNA)
almalinux:python3-unbound1.16.2-19.el9_6.1 · AlmaLinux:9Package registry (OSV)
almalinux:unbound1.16.2-19.el9_6.1 · AlmaLinux:9Package registry (OSV)
almalinux:unbound-anchor1.20.0-12.el10_0 · AlmaLinux:10Package registry (OSV)
almalinux:unbound-devel1.16.2-19.el9_6.1 · AlmaLinux:9Package registry (OSV)
almalinux:unbound-dracut1.16.2-19.el9_6.1 · AlmaLinux:9Package registry (OSV)
almalinux:unbound-libs1.16.2-19.el9_6.1 · AlmaLinux:9Package registry (OSV)
alpine:unbound1.20.0-r2 · Alpine:v3.19Package registry (OSV)
debian:unbound1.17.1-2+deb12u3 · Debian:12Package registry (OSV)
opensuse:unbound1.23.1-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:python3-unbound0:1.16.2-19.el9_6.1 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:python3-unbound-debuginfo0:1.16.2-19.el9_6.1 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:unbound0:1.16.2-19.el9_6.1 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:unbound-anchor0:1.20.0-12.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:unbound-anchor-debuginfo0:1.20.0-12.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:unbound-debuginfo0:1.16.2-19.el9_6.1 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:unbound-debugsource0:1.16.2-19.el9_6.1 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:unbound-devel0:1.16.2-19.el9_6.1 · Red Hat:enterprise_linux:9::crbPackage registry (OSV)
red hat:unbound-dracut0:1.16.2-19.el9_6.1 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:unbound-libs0:1.16.2-19.el9_6.1 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:unbound-libs-debuginfo0:1.16.2-19.el9_6.1 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:unbound-utils-debuginfo0:1.20.0-12.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
rocky linux:unbound0:1.16.2-19.el9_6.1 · Rocky Linux:9Package 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.

No history yet (it accumulates with the daily EPSS job).

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.

  • CVE-2025-1141198 days apartPossible domain hijacking via promiscuous records in the authority section
    22Monitor

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.
  • No special conditions are required; it is repeatable.

If successful

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

Weakness class (CWE)

CWE-349 · Acceptance of Extraneous Untrusted Data With Trusted Data

CVSS vector

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

Show all references (1 more)

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

All records