SIG(0) validation during query flood may lead to undefined behavior (CVE-2026-5947) | HOL Guard CVE

High · CVSS 7.5CVE-2026-5947

SIG(0) validation during query flood may lead to undefined behavior

Answer in brief

CVE-2026-5947 records a High severity (CVSS 7.5) vulnerability in SIG(0) validation during query flood may lead to undefined behavior. The current sources do not mark it as known exploited. The current feed maps ISC/BIND 9 (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published May 20, 2026Updated Aug 24, 2026Source checked Aug 24, 2026First seen by HOL Jul 15, 2026Material review Aug 24, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.5
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps ISC/BIND 9 (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
ISC/BIND 9generic	9.20.0 \|\| 9.21.0 \|\| 9.20.9-S1	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for ISC/BIND 9.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
May 20, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 24, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Jul 15, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.