CVE-2026-5947Network attack vector

Remote service crash via SIG(0) validation race

Published May 20, 2026 · Updated May 20, 2026

Use-after-free in SIG(0) validation in BIND 9 allows remote attackers to crash named via crafted signed DNS traffic. During validation, reaching the recursive-clients limit discards the same DNS message while the validator can still read it. An unauthenticated query flood must hit the limit in the race window; both authoritative servers and resolvers can abort, while code execution is unlikely.

CVSS severity7.5
High
EPSS probability1.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Use-after-free in SIG(0) validation in BIND 9 allows remote attackers to crash named via crafted signed DNS traffic. During validation, reaching the recursive-clients limit discards the same DNS message while the validator can still read it. An unauthenticated query flood must hit the limit in the race window; both authoritative servers and resolvers can abort, while code execution is unlikely.

The record

CVE
CVE-2026-5947
Published
May 20, 2026
Updated
May 20, 2026
Vendor
Internet Systems Consortium
Product
BIND 9
Classifications
CWE-367, CWE-416, CWE-362, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 20, 2026CVE publishedPublication date reported by the CVE source.
  2. May 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=9.20.0 <=9.20.22
  2. Affected versionversion=9.20.9-S1 <=9.20.22-S1
  3. Affected versionversion=9.21.0 <=9.21.21

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Internet Systems Consortium · BIND 9version=9.20.0 <=9.20.22; version=9.20.9-S1 <=9.20.22-S1; version=9.21.0 <=9.21.21

Published CVSS scores

7.5Internet Systems Consortium (ISC)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.9NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5Red Hat Product SecurityCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
CWE-416Use After Free
CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo