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CVE-2026-5950— Unbounded resend loop in BIND 9 resolver

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存在安全漏洞，该漏洞源于解析器状态机中存在无限制的重发循环，可能导致远程未认证攻击者造成严重资源耗尽。以下版本受到影响：9.18.36版本至9.18.48版本、9.20.8版本至9.20.22版本、9.21.7版本至9.21.21版本、9.18.36-S1版本至9.18.48-S1版本和9.20.9-S1版本至9.20.22-S1版本。

CVSS 5.3 · Medium EPSS 0.66% · P50

Affected Version Matrix 5

VendorProduct Version RangeStatus
ISC BIND 9 9.18.36≤ 9.18.48 affected
9.20.8≤ 9.20.22 affected
9.21.7≤ 9.21.21 affected
9.18.36-S1≤ 9.18.48-S1 affected
9.20.9-S1≤ 9.20.22-S1 affected
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I. Basic Information for CVE-2026-5950

Vulnerability Information
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Vulnerability Title
Unbounded resend loop in BIND 9 resolver
Source: CVE Program / CVE List V5
Vulnerability Description
An unbounded resend loop vulnerability exists in the BIND 9 resolver state machine during bad-server handling, enabling a remote unauthenticated attacker to cause severe resource exhaustion by sending queries that trigger specific retry conditions. This issue affects BIND 9 versions 9.18.36 through 9.18.48, 9.20.8 through 9.20.22, 9.21.7 through 9.21.21, 9.18.36-S1 through 9.18.48-S1, and 9.20.9-S1 through 9.20.22-S1.
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:L
Source: CVE Program / CVE List V5
Vulnerability Type
循环条件输入未经检查
Source: CVE Program / CVE List V5
Vulnerability Title
ISC BIND 9 安全漏洞
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存在安全漏洞，该漏洞源于解析器状态机中存在无限制的重发循环，可能导致远程未认证攻击者造成严重资源耗尽。以下版本受到影响：9.18.36版本至9.18.48版本、9.20.8版本至9.20.22版本、9.21.7版本至9.21.21版本、9.18.36-S1版本至9.18.48-S1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 9.18.36 ~ 9.18.48 -

II. Public POCs for CVE-2026-5950

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III. Intelligence Information for CVE-2026-5950

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Patches & Fixes for CVE-2026-5950 (1)

Vendor Advisories for CVE-2026-5950 (1)

Vendor Pages for CVE-2026-5950 (2)

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-2026-5947 7.5 HIGH SIG(0) validation during query flood may lead to undefined behavior
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

IV. Related Vulnerabilities

Same product: BIND 9
Same vendor: ISC
Same weakness: CWE-606

V. Comments for CVE-2026-5950

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