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Vulnerability record · CVE-2026-5947 · published 20 May 2026

CVE-2026-5947: Isc bind race condition vulnerability

Isc · Bind

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.

5.9 CVSS 3.1 Medium EPSS 0.80% · top 45.2% CWE-362 · Race conditionCWE-416 · Use after free
5.9CVSS 3.1 base score
0.80%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
7References
24 Aug 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://downloads.isc.org/isc/bind9/9.20.23 Patch
https://downloads.isc.org/isc/bind9/9.21.22 Patch
https://kb.isc.org/docs/cve-2026-5947 Vendor Advisory
https://access.redhat.com/errata/RHSA-2026:7412
https://access.redhat.com/security/cve/CVE-2026-5947
https://bugzilla.redhat.com/show_bug.cgi?id=2479772
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.json

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

10.0CVE-2008-0122Isc bind vulnerabilityOff-by-one error in the inet_network function in libbind in ISC BIND 9.4.2 and earlier, as used in libc in FreeBSD 6.2 through 7.0-PRERELEASE, allows…EPSS 12%10.0CVE-2001-0010Isc bind vulnerabilityBuffer overflow in transaction signature (TSIG) handling code in BIND 8 allows remote attackers to gain root privileges.EPSS 32%10.0CVE-2001-0011Isc bind vulnerabilityBuffer overflow in nslookupComplain function in BIND 4 allows remote attackers to gain root privileges.EPSS 7.7%10.0CVE-2001-0013Isc bind vulnerabilityFormat string vulnerability in nslookupComplain function in BIND 4 allows remote attackers to gain root privileges.EPSS 11%10.0CVE-2000-1029Isc bind vulnerabilityBuffer overflow in host command allows a remote attacker to execute arbitrary commands via a long response to an AXFR query.EPSS 14%10.0CVE-1999-0837Isc bind vulnerabilityDenial of service in BIND by improperly closing TCP sessions via so_linger.EPSS 2.7%10.0CVE-1999-0009Data general dg ux vulnerabilityInverse query buffer overflow in BIND 4.9 and BIND 8 Releases.EPSS 29%9.8CVE-2026-3593Isc bind use after free vulnerabilityA use-after-free vulnerability exists within the DNS-over-HTTPS implementation. This issue affects BIND 9 versions 9.20.0 through 9.20.22, 9.21.0 thr…EPSS 1.1%

Source: NIST National Vulnerability Database (record CVE-2026-5947), CISA KEV, FIRST EPSS (scores of 2026-09-29). This page is refreshed as NVD updates the record.