ISC BIND up to 9.21.21 DNS Message race condition

CVSS Meta Temp Score
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CTI Interest Score
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6.2$0-$5k0.00

Summaryinfo

A vulnerability categorized as problematic has been discovered in ISC BIND up to 9.18.48/9.18.49-S0/9.20.22/9.20.22-S1/9.21.21. The affected element is an unknown function of the component DNS Message Handler. Executing a manipulation can lead to race condition. This vulnerability is handled as CVE-2026-5947. The attack can be executed remotely. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in ISC BIND up to 9.18.48/9.18.49-S0/9.20.22/9.20.22-S1/9.21.21. It has been declared as problematic. This vulnerability affects an unknown functionality of the component DNS Message Handler. The manipulation with an unknown input leads to a race condition vulnerability. The CWE definition for the vulnerability is CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is shared for download at kb.isc.org. This vulnerability was named CVE-2026-5947 since 04/09/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 06/05/2026).

The vulnerability scanner Nessus provides a plugin with the ID 315662 (ISC BIND 9.20.0 < 9.20.23 / 9.20.9-S1 < 9.20.23-S1 / 9.21.0 < 9.21.22 Vulnerability (cve-2026-5947)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 9.18.49 or 9.18.49-S1 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (315662) and CERT Bund (WID-SEC-2026-1626). Once again VulDB remains the best source for vulnerability data.

Affected

  • Debian Linux
  • Red Hat Enterprise Linux
  • Fedora Linux
  • Ubuntu Linux
  • Oracle Linux
  • Infoblox NIOS
  • SUSE openSUSE
  • Internet Systems Consortium BIND

Productinfo

Type

Vendor

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.2
VulDB Meta Temp Score: 6.2

VulDB Base Score: 5.3
VulDB Temp Score: 5.1
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.9
NVD Vector: 🔒

CNA Base Score: 7.5
CNA Vector (isc): 🔒

CVSSv2info

AVACAuCIA
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Race condition
CWE: CWE-362
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 315662
Nessus Name: ISC BIND 9.20.0 < 9.20.23 / 9.20.9-S1 < 9.20.23-S1 / 9.21.0 < 9.21.22 Vulnerability (cve-2026-5947)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: BIND 9.18.49/9.18.49-S1

Timelineinfo

04/09/2026 CVE reserved
05/20/2026 +41 days Advisory disclosed
05/20/2026 +0 days VulDB entry created
06/05/2026 +16 days VulDB entry last update

Sourcesinfo

Vendor: isc.org

Advisory: kb.isc.org
Status: Confirmed

CVE: CVE-2026-5947 (🔒)
GCVE (CVE): GCVE-0-2026-5947
GCVE (VulDB): GCVE-100-364876
CERT Bund: WID-SEC-2026-1626 - Internet Systems Consortium BIND: Mehrere Schwachstellen

Entryinfo

Created: 05/20/2026 15:40
Updated: 06/05/2026 14:31
Changes: 05/20/2026 15:40 (64), 05/20/2026 23:54 (2), 05/21/2026 18:37 (7), 05/23/2026 22:24 (11), 05/26/2026 15:40 (1), 06/05/2026 14:31 (1)
Complete: 🔍
Cache ID: 216::103

Once again VulDB remains the best source for vulnerability data.

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