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CVE-2026-5947— SIG(0) validation during query flood may lead to undefined behavior

Quick assessment

Affected
ISC BIND 9
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.

ISC BIND 9是ISC组织的一个域名系统软件。 ISC BIND 9存在竞争条件问题漏洞，该漏洞源于竞争条件导致释放后重用，可能导致未定义行为。以下版本受到影响：9.20.0版本至9.20.22版本、9.21.0版本至9.21.21版本和9.20.9-S1版本至9.20.22-S1版本。

CVSS 7.5 · High EPSS 0.80% · P55

Possible ATT&CK Techniques 1 AI

T1498 · Network Denial of Service

Affected Version Matrix 5

VendorProduct Version RangeStatus
ISC BIND 9 9.20.0≤ 9.20.22 affected
9.21.0≤ 9.21.21 affected
9.20.9-S1≤ 9.20.22-S1 affected
9.18.28≤ 9.18.49 unaffected
9.18.28-S1≤ 9.18.49-S1 unaffected
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I. Basic Information for CVE-2026-5947

Vulnerability Information
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Vulnerability Title
SIG(0) validation during query flood may lead to undefined behavior
Source: CVE Program / CVE List V5
Vulnerability Description
Undefined behavior may result due to a race condition leading to a use-after-free violation. If BIND receives an incoming DNS message signed with SIG(0), it begins work to validate that signature. If, during that validation, the "recursive-clients" limit is reached (as would occur during a query flood), and that same DNS message is discarded per the limit, there is a brief window of time while the SIG(0) validation may attempt to read the now-discarded DNS message. This issue affects BIND 9 versions 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and 9.20.9-S1 through 9.20.22-S1. BIND 9 versions 9.18.28 through 9.18.49 and 9.18.28-S1 through 9.18.49-S1 are NOT affected.
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
使用共享资源的并发执行不恰当同步问题(竞争条件)
Source: CVE Program / CVE List V5
Vulnerability Title
ISC BIND 9 竞争条件问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
ISC BIND 9是ISC组织的一个域名系统软件。 ISC BIND 9存在竞争条件问题漏洞，该漏洞源于竞争条件导致释放后重用，可能导致未定义行为。以下版本受到影响：9.20.0版本至9.20.22版本、9.21.0版本至9.21.21版本和9.20.9-S1版本至9.20.22-S1版本。
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
ISC BIND 9 9.20.0 ~ 9.20.22 -

II. Public POCs for CVE-2026-5947

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III. Intelligence Information for CVE-2026-5947

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Patches & Fixes for CVE-2026-5947 (1)

Vendor Advisories for CVE-2026-5947 (1)

Vendor Pages for CVE-2026-5947 (1)

Same Patch Batch · ISC · 2026-05-20 · 6 CVEs total

CVE-2026-3039 7.5 HIGH BIND 9 server memory exhaustion during GSS-API TKEY negotiation
CVE-2026-5946 7.5 HIGH Invalid handling of CLASS != IN
CVE-2026-3593 7.4 HIGH Heap use-after-free vulnerability in BIND 9 DNS-over-HTTPS implementation
CVE-2026-3592 5.3 MEDIUM Amplification vulnerabilities via self-pointed glue records
CVE-2026-5950 5.3 MEDIUM Unbounded resend loop in BIND 9 resolver

IV. Related Vulnerabilities

Same product: BIND 9
Same vendor: ISC
Same weakness: CWE-362

V. Comments for CVE-2026-5947

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