Trending
CVE-2026-42959

CVE detail

CVE-2026-42959

NLnet Labs Unbound up to and including version 1.25.0 has a denial of service vulnerability in the DNSSEC validator that can lead to a crash given malicious upstream replies. When Unbound constructs chase-reply messages for validation, the code uses the wrong counter to calculate write offsets for ADDITIONAL section rrsets. DNAME duplication could increase the ANSWER section count and authority filtering could decrease the AUTHORITY section count and create an uninitialized array slot. Combining these two, the validator later dereferences this uninitialized pointer, causing an immediate process crash. An adversary controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue records. Unbound 1.25.1 contains a patch with a fix to use the proper counters to calculate the write offsets.

CVSS 8.7 · HighBuzz score 41.0

Buzz score

Why this CVE is surfacing

Buzz score total 41.0

This all-time snapshot uses the same composite formula as Trending across a 30-year evidence window, rather than a current rolling window.

Buzz score components · mention 23.0 · diversity 18.0 · KEV 0.0 · OTX 0.0 · PoC 0.0

Mention score

23.0

9 evidence mentions in the snapshot

Diversity score

18.0

5 sources across 3 categories

KEV score

0.0

No KEV entry observed

OTX score

0.0

0 OTX pulses

PoC score

0.0

0 repos · best confidence N/A

Best PoC traction

Maximum stars on a matched PoC repo

Why it matters now

Mention timeline

Total mentions: 0; within the 30d window
Peak daily: 0; highest bucket

Evidence

Source links by recency

Newest mentions first

9 source links · newest first

CVE-2026-42959 Crash during DNSSEC validation of malicious contentMicrosoft MSRC
Information published.
vendormsrc.microsoft.comMay 21, 2026, 8:02 AM
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42959.jsonsecurity.access.redhat.com
No excerpt available.
Vendor Advisorysecurity.access.redhat.comMay 20, 2026, 10:16 AM
https://bugzilla.redhat.com/show_bug.cgi?id=2479806bugzilla.redhat.com
No excerpt available.
Exploitbugzilla.redhat.comMay 20, 2026, 10:16 AM
https://access.redhat.com/security/cve/CVE-2026-42959access.redhat.com
No excerpt available.
Vendor Advisoryaccess.redhat.comMay 20, 2026, 10:16 AM
https://access.redhat.com/errata/RHSA-2026:24369access.redhat.com
No excerpt available.
Vendor Advisoryaccess.redhat.comMay 20, 2026, 10:16 AM
https://access.redhat.com/errata/RHSA-2026:24365access.redhat.com
No excerpt available.
Vendor Advisoryaccess.redhat.comMay 20, 2026, 10:16 AM
https://access.redhat.com/errata/RHSA-2026:23231access.redhat.com
No excerpt available.
Vendor Advisoryaccess.redhat.comMay 20, 2026, 10:16 AM
https://access.redhat.com/errata/RHSA-2026:19752access.redhat.com
No excerpt available.
Vendor Advisoryaccess.redhat.comMay 20, 2026, 10:16 AM
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42959.txtwww.nlnetlabs.nl
No excerpt available.
Vendor Advisorywww.nlnetlabs.nlMay 20, 2026, 10:16 AM

Exploit code

Public exploit repository references

Public PoC repositories are third-party, potentially unsafe artifacts. Treat their code as untrusted and use it only on authorized systems in an isolated, least-privilege environment. cvebuzz does not execute the code or verify that an exploit works.

0 repository references · best confidence N/A · max 0 stars

No public PoC repositories have been matched yet.

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External lookup

Potential internet exposure

Potential exposure only — not proof of vulnerability.Shodan results indicate potentially internet-exposed products, not confirmed vulnerable systems. They do not confirm that any returned system is vulnerable to CVE-2026-42959.

Product-level CPE searches intentionally omit version fields and NVD version-range or configuration certainty. Verify the exact product version and configuration independently.

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Product CPE queries

Derived from this CVE's existing NVD CPE 2.3 records; the application, operating-system, or hardware part is retained.

cpe:2.3:a:nlnetlabs:unboundSearch this product on Shodan

Exact CVE query

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vuln:CVE-2026-42959Search this CVE on Shodan

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Metadata

Canonical fields

NVD status

Modified

Published

May 20, 2026

Modified

Jul 24, 2026

Official record

Authoritative NVD record

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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:X/V:X/RE:X/U:Red

CWE IDs

Vendor classifications

How this vector reads

CVSS 4.0 base metrics decoded below. This explanation does not recalculate or change the NVD score.

Attack Vector (AV): Network. The vulnerable system can be reached across network boundaries.
Attack Complexity (AC): Low. No special conditions beyond the attacker-controlled steps are required.
Attack Requirements (AT): None. No prerequisite deployment or execution condition is required.
Privileges Required (PR): None. The attacker needs no privileges on the vulnerable system.
User Interaction (UI): None. Exploitation does not require a targeted user to act.
Vulnerable System Confidentiality (VC): None. There is no direct impact to this security property.
Vulnerable System Integrity (VI): None. There is no direct impact to this security property.
Vulnerable System Availability (VA): High. There is a total or serious impact to this security property.
Subsequent System Confidentiality (SC): None. There is no direct impact to this security property.
Subsequent System Integrity (SI): None. There is no direct impact to this security property.
Subsequent System Availability (SA): None. There is no direct impact to this security property.

Optional CVSS v4 metrics remain in the raw vector; only base metrics are expanded here.

Signals

Exploitation indicators

0 stored signals · no KEV · 0 OTX pulses