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VulnerabilityPublished Updated

CVE-2026-5947: ISC BIND 9 · Race Condition

Affects ISC BIND 9Source CVE Database V5

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Not known to be exploited · CVSS 7.5 High : upgrade to 9.21.22 or 9.20.23 soon.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
1.3% chance of exploitation in 30 days – higher than 72% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 9.21.22, 9.20.23
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 20 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

What to do

Upgrade isc/bind9 to 9.21.22 or 9.20.23.

Affected software

ProductAffectedFixed in
ISCBIND 9Affected
  • >=9.20.0 <=9.20.22
  • >=9.21.0 <=9.21.21
  • >=9.20.9-S1 <=9.20.22-S1
Fixed in–
GitHubisc/bind9pkg:github/isc/bind9Other threatsAffected
  • <9.20.23
  • <9.21.22
Fixed in
  • 9.20.23
  • 9.21.22

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

The Red Hat advisories referencing this CVE do not currently list a fix or updated packages addressing this vulnerability. If you cannot patch yet, consider limiting exposure to query floods that might trigger the recursive-clients limit or implement network-level protections to mitigate query floods.

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.

References

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