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CVE-2026-44390— Unbounded name compression in certain cases causes degradation of service

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及之前版本存在安全漏洞，该漏洞源于处理大型RRset时名称压缩操作未绑定，可能导致性能下降和拒绝服务。

CVSS 6.9 · Medium 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-2026-44390

Vulnerability Information
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Vulnerability Title
Unbounded name compression in certain cases causes degradation of service
Source: CVE Program / CVE List V5
Vulnerability Description
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability when handling replies with very large RRsets that Unbound needs to perform name compression for. Malicious upstream responses with very large RRsets with records that don't share a suffix above the root can cause Unbound to spend a considerable time applying name compression to downstream replies. This can lead to degraded performance and eventually denial of service in well orchestrated attacks. An adversary can exploit the vulnerability by querying Unbound for the specially crafted contents of a malicious zone with very large RRsets. Before Unbound replies to the query it will try to apply name compression which was an unbounded operation that could lock the CPU until the whole packet was complete. A compression limit was introduced in 1.21.1 for this but it didn't account for the case where records would not share any suffix above the root. That causes Unbound to go in a different code path because of the compression tree lookup failure and eventually not increment the compression counter for those operations. Unbound 1.25.1 contains a patch with a fix that increments the compression counter regardless of the compression tree lookup. This is a complement fix to CVE-2024-8508.
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:L/SC:N/SI:N/SA:N/U:Amber
Source: CVE Program / CVE List V5
Vulnerability Type
算法复杂性
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 1.25.0及之前版本存在安全漏洞，该漏洞源于处理大型RRset时名称压缩操作未绑定，可能导致性能下降和拒绝服务。
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-2026-44390

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III. Intelligence Information for CVE-2026-44390

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Vendor Advisories for CVE-2026-44390 (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-2026-42944 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-2026-41292 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-407

V. Comments for CVE-2026-44390

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