Undefined behavior may result due to a race condition leading to a use-after-free violation. If...

CVE-2026-5947 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

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.

Basic information

Type
unreviewed
Severity
high
Advisory on GitHub
Open advisory ↗
Repository advisory
—
Source code
Not specified
Published (advisory)
2026-05-20 15:35:33 UTC
Updated
2026-06-30 03:36:46 UTC
NVD published
2026-05-20

EPSS Score

Score Percentile
1.39% 68.82%

CVSS Scores

Base score Version Severity Vector
7.5 3.1 —
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.

Identifiers

Type Value
GHSA GHSA-6mm6-m775-chpm ↗
CVE CVE-2026-5947 ↗

CWEs

CWE id Name
CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition

References

cvelogic Threat Intelligence