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CVE-2026-55973— 'dns-error-reporting: yes' leads to stack buffer overflow

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是荷兰NLnet Labs组织的域名系统解析服务器。 NLnet Labs Unbound 1.23.0版本至1.25.1版本存在输入验证错误漏洞，该漏洞源于当启用‘dns-error-reporting: yes’时，程序读取上游响应的EDNS Report-Channel选项（代码18）并用其长度作为代理域长度，在对代理域执行域名检查时未使用返回长度，导致若代理域后存在垃圾数据，这些字节被移至‘_er.’报告查询名称尾部，后续在‘find_closest_of_ty

CVSS 7.5 · High EPSS 0.28% · P21

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
NLnet Labs Unbound 1.23.0< 1.25.2 affected
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I. Basic Information for CVE-2026-55973

Vulnerability Information
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Vulnerability Title
'dns-error-reporting: yes' leads to stack buffer overflow
Source: CVE Program / CVE List V5
Vulnerability Description
In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during 'find_closest_of_type()', it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to 'dname_query_hash()' as a label length writing over the stack variable 'labuf'. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
输入验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
NLnet Labs Unbound 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
NLnet Labs Unbound是荷兰NLnet Labs组织的域名系统解析服务器。 NLnet Labs Unbound 1.23.0版本至1.25.1版本存在输入验证错误漏洞，该漏洞源于当启用‘dns-error-reporting: yes’时，程序读取上游响应的EDNS Report-Channel选项（代码18）并用其长度作为代理域长度，在对代理域执行域名检查时未使用返回长度，导致若代理域后存在垃圾数据，这些字节被移至‘_er.’报告查询名称尾部，后续在‘find_closest_of_ty
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 1.23.0 ~ 1.25.2 -

II. Public POCs for CVE-2026-55973

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III. Intelligence Information for CVE-2026-55973

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Other References for CVE-2026-55973 (1)

Same Patch Batch · NLnet Labs · 2026-07-22 · 24 CVEs total

CVE-2026-32665 7.5 HIGH Remote DNS-over-QUIC denial of service due to `quic-size` budget bypass
CVE-2026-40691 7.5 HIGH Packet of death for DNSCrypt over TCP
CVE-2026-44690 7.5 HIGH Cross-zone wildcard cache poisoning via RRSIG.labels manipulation
CVE-2026-50248 6.5 MEDIUM BOGUS configured primary hostname accepted for XFR in auth/rpz zones
CVE-2026-55717 5.9 MEDIUM 'serve-expired-client-timeout' and 'response-ip' CNAME redirect could lead to a crash
CVE-2026-55991 5.9 MEDIUM Remote DNS-over-QUIC (DoQ) flow-control assertion failure in libngtcp2
CVE-2026-55990 5.9 MEDIUM Packet of death for a DNSCrypt misconfigured Unbound
CVE-2026-56444 5.9 MEDIUM Degradation of resolution service when 'discard-timeout' and 'serve-expired-client-timeout
CVE-2026-14586 5.9 MEDIUM Assertion in libngtcp2 when under pressure in high concurrency DNS-over-QUIC environments
CVE-2026-44621 5.9 MEDIUM Libunbound applications configured with 'unwanted-reply-threshold' could eventually be abr
CVE-2026-50046 5.9 MEDIUM Possible heap use-after-free in an error path when a DoT forwarded query is jostled out
CVE-2026-52863 5.9 MEDIUM Memory corruption could lead to crash and denial of service
CVE-2026-50045 5.3 MEDIUM 'max-global-quota' reset by DNSSEC validation restarts
CVE-2026-50251 5.3 MEDIUM Attacker supplied '0.0.0.0'/'::' glue triggers defensive full-cache flush
CVE-2026-56416 4.8 MEDIUM Possible heap buffer overflow when validator canonicalizes RDATA that contains domain name
CVE-2026-46582 3.7 LOW A wildcard replay, as another piece of data, triggers poisoning in the serve expired reply
CVE-2026-44687 3.7 LOW Off-by-one error in 'harden-below-nxdomain' logic can shadow a stub/forward zone by a legi
CVE-2026-54478 3.7 LOW DNS Cookie bypass when combined with proxy-protocol use
CVE-2026-42955 3.7 LOW Extra fix for CVE-2026-40622 to also clamp the TTL of A/AAAA records disallowing a one-tim
CVE-2026-41637 3.7 LOW Degradation of resolution service from improperly accounted client-terminated DNS-over-QUI

Showing top 20 of 24 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Unbound
Same vendor: NLnet Labs
Same weakness: CWE-20

V. Comments for CVE-2026-55973

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