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CVE.org (no NVD analysis yet)· CNA NLnet Labs

CVE-2026-109125: Possible cache poisoning vulnerability via a cache side-channel exposed by 'unwanted-reply-threshold'

MediumCVSS 5.3 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 21/100)

  • 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: 0.17% (FIRST EPSS).
  • Someone on the same network segment 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 1.26.2.

Low priority for now. Upgrade to NLnet Labs Unbound 1.26.2 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 up to and including version 1.26.1, an observable cache-level side-channel can be exposed with 'unwanted-reply-threshold > 0' configurations (not a default configuration). If a response-like UDP datagram reaches the upstream source port currently used by a recursive query, but its TXID does not match any pending query, Unbound counts the packet as an unwanted reply. When the accumulated count reaches the configured threshold, Unbound clears the worker's RRset cache and message cache. This cache clear action does not destroy the current upstream UDP pending query. Therefore, an external observer can distinguish whether a candidate port matches the current upstream source port by checking whether an existing cached item has been cleared. This is a cache side-channel vulnerability that can be used to probe the upstream source port. Although the attack is not feasible on default configurations and the suggested value (10 million) makes it an ureliable attack on a public resolver, in scenarios where the attacker can keep a concurrent query window alive, the attacker can first filter the source port and then perform birthday-style guessing against the TXID, making cache poisoning a feasible attack path.

Published
Oct 21, 2026
Updated
Oct 29, 2026
EPSS
0.1% · 6th percentile

Report tools

JSON

Action score

21

Monitor

Low priority for now.

CVSS
21 / 40 · 5.3 / 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
5.3
NVD has not scored this yet; the score shown is the CNA’s.

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

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  • 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 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

    • before 1.26.2affected · semver

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:12unboundfrom 0—
Debian:13unboundbefore 1.26.2-0+deb13u11.26.2-0+deb13u1
Debian:14unboundbefore 1.26.2-11.26.2-1
openSUSE:Tumbleweedunboundbefore 1.26.2-1.11.26.2-1.1

Same product

nlnet labs: all records

Other highest-scoring records for the same primary product.

  • CVE-2025-5994Cache poisoning via the ECS-enabled Rebirthday Attack
    34Monitor
  • 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

Published before and after this one in the same product

  • ← EarlierCVE-2025-11411Oct 22, 2025 · Possible domain hijacking via promiscuous records in the authority section
    22Monitor
  • ← EarlierCVE-2026-14586Jul 22, 2026 · Assertion in libngtcp2 when under pressure in high concurrency DNS-over-QUIC environments
    23Monitor
  • 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 Unbound1.26.2Vendor (CNA)
debian:unbound1.26.2-0+deb13u1 · Debian:13Package registry (OSV)
opensuse:unbound1.26.2-1.1 · openSUSE:TumbleweedPackage 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.

  1. Published
  2. Fix recordedsame day
  3. TodayNov 13, 2026+23 d
EPSS, last 120 days

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

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: patch commit or PR link · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Someone on the same network segment 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
none
Integrity
high · data or configuration can be modified
Availability
none
Attack vector
Adjacent
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
High
Availability impact
None

Weakness class (CWE)

CWE-205 · Observable Behavioral Discrepancy

CVSS vector

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

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. SSVC exploitation— → none
  2. Exploit maturity— → none
  3. 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