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CVE-2026-42959— Crash during DNSSEC validation of malicious content

Quick assessment

Affected
NLnet Labs Unbound
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

NLnet Labs Unbound是NLnet Labs开源的一个高性能DNS解析器。 NLnet Labs Unbound 1.25.0及之前版本存在缓冲区错误漏洞，该漏洞源于DNSSEC验证器中使用错误计数器计算写入偏移量，导致未初始化指针被引用，可能造成进程崩溃。

CVSS 8.7 · High EPSS 0.72% · P52

Possible ATT&CK Techniques 1 AI

T1498.002 · Reflection Amplification

Affected Version Matrix 1

VendorProduct Version RangeStatus
NLnet Labs Unbound < 1.25.1 affected
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I. Basic Information for CVE-2026-42959

Vulnerability Information
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Vulnerability Title
Crash during DNSSEC validation of malicious content
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
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/U:Red
Source: CVE Program / CVE List V5
Vulnerability Type
使用未经初始化的指针
Source: CVE Program / CVE List V5
Vulnerability Title
NLnet Labs Unbound 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
NLnet Labs Unbound是NLnet Labs开源的一个高性能DNS解析器。 NLnet Labs Unbound 1.25.0及之前版本存在缓冲区错误漏洞，该漏洞源于DNSSEC验证器中使用错误计数器计算写入偏移量，导致未初始化指针被引用，可能造成进程崩溃。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
NLnet Labs Unbound 0 ~ 1.25.1 -

II. Public POCs for CVE-2026-42959

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III. Intelligence Information for CVE-2026-42959

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Vendor Advisories for CVE-2026-42959 (1)

Same Patch Batch · NLnet Labs · 2026-05-20 · 11 CVEs total

CVE-2026-33278 9.1 CRITICAL Possible arbitrary code execution during DNSSEC validation
CVE-2026-42944 8.7 HIGH Heap overflow with multiple NSID, COOKIE, PADDING EDNS options
CVE-2026-42534 6.9 MEDIUM Jostle logic bypass degrades resolution performance
CVE-2026-44390 6.9 MEDIUM Unbounded name compression in certain cases causes degradation of service
CVE-2026-41292 6.6 MEDIUM Long list of incoming EDNS options degrades performance
CVE-2026-42923 Degradation of service with unbounded NSEC3 hash calculations
CVE-2026-42960 Possible cache poisoning via promiscuous records for the authority section
CVE-2026-32792 Packet of death with DNSCrypt
CVE-2026-40622 Another 'ghost domain names' attack variant
CVE-2026-44608 Use after free and crash under special conditions in RPZ code

IV. Related Vulnerabilities

Same product: Unbound
Same vendor: NLnet Labs
Same weakness: CWE-824

V. Comments for CVE-2026-42959

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