CVE-2026-5947
SIG(0) validation during query flood may lead to undefined behavior
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.
INFO
Published Date :
May 20, 2026, 1:16 p.m.
Last Modified :
May 21, 2026, 3:24 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update BIND to a version not affected by this issue.
- Apply vendor-provided patches for your BIND version.
- Restart the BIND service after updating.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-5947.
| URL | Resource |
|---|---|
| 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 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-5947 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-5947
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-5947 vulnerability anywhere in the article.
-
CybersecurityNews
BIND 9 Software Vulnerabilities Exposes Resolvers and Authoritative Servers to Remote Exploits
A series of newly documented vulnerabilities in ISC BIND 9 has raised significant security concerns for DNS infrastructure operators, with multiple flaws enabling denial-of-service (DoS) attacks, memo ... Read more
The following table lists the changes that have been made to the
CVE-2026-5947 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
May. 21, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Added CPE Configuration OR *cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:* versions from (including) 9.20.0 up to (excluding) 9.20.23 *cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:* versions from (including) 9.21.0 up to (excluding) 9.21.22 Added Reference Type Internet Systems Consortium (ISC): https://downloads.isc.org/isc/bind9/9.20.23 Types: Patch Added Reference Type Internet Systems Consortium (ISC): https://downloads.isc.org/isc/bind9/9.21.22 Types: Patch Added Reference Type Internet Systems Consortium (ISC): https://kb.isc.org/docs/cve-2026-5947 Types: Vendor Advisory -
New CVE Received by [email protected]
May. 20, 2026
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-362 Added CWE CWE-416 Added Reference https://downloads.isc.org/isc/bind9/9.20.23 Added Reference https://downloads.isc.org/isc/bind9/9.21.22 Added Reference https://kb.isc.org/docs/cve-2026-5947