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CVE-2026-42944— Heap overflow with multiple NSID, COOKIE, PADDING EDNS options

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 1.14.0版本至1.25.0版本存在安全漏洞，该漏洞源于编码多个NSID和/或DNS Cookie EDNS和/或EDNS Padding选项时大小计算截断导致堆溢出，攻击者通过附加多个选项到查询可触发堆溢出写入并导致崩溃。

CVSS 8.7 · High EPSS 0.78% · P54

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
NLnet Labs Unbound 1.14.0< 1.25.1 affected
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I. Basic Information for CVE-2026-42944

Vulnerability Information
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Vulnerability Title
Heap overflow with multiple NSID, COOKIE, PADDING EDNS options
Source: CVE Program / CVE List V5
Vulnerability Description
NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.
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
数值截断错误
Source: CVE Program / CVE List V5
Vulnerability Title
NLnet Labs Unbound 安全漏洞
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 1.14.0版本至1.25.0版本存在安全漏洞，该漏洞源于编码多个NSID和/或DNS Cookie EDNS和/或EDNS Padding选项时大小计算截断导致堆溢出，攻击者通过附加多个选项到查询可触发堆溢出写入并导致崩溃。
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 1.14.0 ~ 1.25.1 -

II. Public POCs for CVE-2026-42944

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III. Intelligence Information for CVE-2026-42944

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Other References for CVE-2026-42944 (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-2026-42959 8.7 HIGH Crash during DNSSEC validation of malicious content
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-197

V. Comments for CVE-2026-42944

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