Security readout for executives and security teams
Plain-English summary
A remote, unauthenticated attacker could potentially disrupt vulnerable BIND 9 DNS services by combining SIG(0)-signed DNS messages with enough traffic to exhaust the recursive-client limit. A race condition can then access discarded memory, causing undefined behavior and threatening DNS availability. The supplied evidence does not establish data theft, record manipulation, or active exploitation.
Executive priority
Treat this as a high-priority availability risk for vulnerable production DNS infrastructure. Patch exposed or business-critical servers promptly because DNS disruption can affect many dependent services. Emergency incident escalation is not justified solely by the supplied evidence, which shows no confirmed active exploitation, but query-flood exposure and operational criticality should shorten remediation timelines.
Technical view
During SIG(0) validation, BIND may discard the same DNS message when the recursive-clients limit is reached. A brief race window can then produce a use-after-free read and undefined behavior. CVSS 3.1 is 7.5: network-accessible, low complexity, no privileges or interaction, with high availability impact only.
Likely exposure
Exposure is limited to BIND 9 versions 9.20.0–9.20.22, 9.21.0–9.21.21, and 9.20.9-S1–9.20.22-S1 receiving relevant DNS traffic. Versions 9.18.28–9.18.49 and corresponding S1 releases are explicitly unaffected. Internet-accessible DNS services and systems susceptible to recursive-client saturation warrant prompt review.
Exploitation context
The condition requires a SIG(0)-signed incoming DNS message, concurrent validation, and exhaustion of the recursive-clients limit, such as during a query flood. The CVSS assessment treats exploitation as remotely reachable and low complexity. The bundle marks KEV false and provides no cited evidence of active exploitation; real-world exploitation status therefore remains unconfirmed.
Researcher notes
The relevant weakness chain is concurrency-related: race and time-of-check/time-of-use behavior culminate in use-after-free access. The documented outcome is undefined behavior, while the CVSS vector claims availability impact without confidentiality or integrity impact. Sources do not specify a reliable crash signature, exploitation prevalence, or whether memory access can produce consequences beyond denial of service.
Mitigation direction
- Upgrade 9.20 deployments to BIND 9.20.23 or a later vendor-approved fixed release.
- Upgrade 9.21 deployments to BIND 9.21.22 or a later vendor-approved fixed release.
- For S1 or packaged distributions, follow ISC or distributor guidance for the appropriate fixed build.
- Apply Red Hat RHSA-2026:7412 where its listed packages and systems are applicable.
- Prioritize externally reachable DNS servers and maintain service resilience while updates are deployed.
Validation and detection
- Inventory BIND versions across authoritative, recursive, forwarding, and internally managed DNS servers.
- Confirm no installation falls within the affected version ranges.
- Verify upgraded binaries or packages match ISC or distributor fixed-release guidance.
- Review DNS telemetry for query floods, recursive-client saturation, crashes, or unexpected restarts.
- Confirm explicitly unaffected 9.18 installations have not been misclassified as vulnerable.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-362: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCWE-367: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCWE-416: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-5947 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
2 official scoresWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6iscCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADPVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- ADP timelineredhat-SADP
Reported to Red Hat.
- CVE publishedCVE Program
The CVE record was published.
- ADP timelineredhat-SADP
Made public.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2026-05-19T09:59:51.277Z: Reported to Red Hat.
- 2026-05-21T12:15:50.513Z: Made public.
Source materials
- CVE List V5 sourceCVE List V5
- CVE-2026-5947CVE reference, isc · vendor-advisory
- https://downloads.isc.org/isc/bind9/9.20.23CVE reference, isc · patch
- https://downloads.isc.org/isc/bind9/9.21.22CVE reference, isc · patch
- https://access.redhat.com/security/cve/CVE-2026-5947CVE reference, redhat-SADP · vdb-entry, x_refsource_REDHAT
- RHBZ#2479772CVE reference, redhat-SADP · issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.jsonCVE reference, redhat-SADP · x_sadp-csaf-vex
- https://access.redhat.com/errata/RHSA-2026:7412CVE reference, redhat-SADP · vendor-advisory, x_refsource_REDHAT
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Time-of-check Time-of-use (TOCTOU) Race Condition
Time-of-check Time-of-use (TOCTOU) Race Condition represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.