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    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.

    Published:May 20, 2026
    Last Modified:May 20, 2026
    EPS:May 20, 2026
    EPSS Score:0.00042
    CVSS Score:7.5

    Affected Products

    Vendor
    Nlnetlabs
    Product
    Unbound

    Exploits

    No exploit reference

    Common Weakness Enumeration

    CWE-824 Access of Uninitialized Pointer

    Common Attack Pattern Enumeration and Classification (CAPEC)

    No CAPEC recorded yet

    Related CVEs

    CVE-2026-56444 (CVSS 5.9) — In NLnet Labs Unbound 1.20.0 up to and including 1.25.1, when Unbound is configured with 'serve-expired: yes' …
    CVE-2026-56416 (CVSS 4.8) — In NLnet Labs Unbound up to and including version 1.25.1, when the validator builds the canonical RDATA form f…
    CVE-2026-55991 (CVSS 5.9) — In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, a remote unauthenticated client can trigger a libngtc…
    CVE-2026-55990 (CVSS 5.9) — In NLnet Labs Unbound 1.7.0 up to and including 1.25.1, when the 'dnscrypt:' clause lists more 'dnscrypt-provi…
    CVE-2026-55717 (CVSS 5.9) — In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'res…
    CVE-2026-55708 (CVSS 3.1) — In NLnet Labs Unbound 1.6.0 up to and including 1.25.1, the 'view_local_data' and 'view_local_datas' commands …
    CVE-2026-54478 (CVSS 3.7) — In NLnet Labs Unbound 1.18.0 up to and including 1.25.1, when Unbound listens on a 'proxy-protocol-port' inter…
    CVE-2026-52863 (CVSS 5.9) — In NLnet Labs Unbound 1.25.0 up to and including 1.25.1, a fix that makes the 'respip' and 'dns64' modules wor…
    CVE-2026-50252 (CVSS 5.7) — In NLnet Labs Unbound 1.4.22 up to and including 1.25.1, UDP source port is randomized and intended to serve a…
    CVE-2026-50251 (CVSS 5.3) — In NLnet Labs Unbound up to and including version 1.25.1, when 'unwanted-reply-threshold' is enabled (set to a…

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High