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BindApplication · Isc

CVE-2026-5950

MEDIUM · 5.3 CVSS v3.1 Published 2026-05-20
Fix available
A fix is available. Upgrade to 9.18.49 / 9.20.23 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
An unbounded resend loop vulnerability exists in the BIND 9 resolver state machine during bad-server handling, enabling a remote unauthenticated attacker to cause severe resource exhaustion by sending queries that trigger specific retry conditions. This issue affects BIND 9 versions 9.18.36 through 9.18.48, 9.20.8 through 9.20.22, 9.21.7 through 9.21.21, 9.18.36-S1 through 9.18.48-S1, and 9.20.9-S1 through 9.20.22-S1.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis

A detailed technical summary for this CVE is being prepared.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
BindApplication
Affected:>= 9.18.36, < 9.18.49>= 9.20.8, < 9.20.23>= 9.21.7, < 9.21.21

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 9.18.49 / 9.20.23 / 9.21.21 or later
Fixed in 9.18.499.20.239.21.21
Vendor patch downloads.isc.org →
Recommended fix High confidence

9.18.49, 9.20.23, 9.21.21, or any subsequent release

  1. 1. Backup your current BIND 9 configuration files (typically in /etc/named.conf and /etc/bind/ or /var/named/ depending on your OS).
  2. 2. Download the fixed BIND 9 version from the ISC downloads page. For version 9.18.x, use 9.18.49 or later; for 9.20.x, use 9.20.23 or later; for 9.21.x, use 9.21.21 or later.
  3. 3. Stop the BIND named service: 'systemctl stop named' or 'service named stop' depending on your system.
  4. 4. Install the new BIND 9 package using your system's package manager (e.g., apt, yum, dnf) or compile from source if using manual installation.
  5. 5. Restore your backed-up configuration files to ensure your existing configuration is preserved.
  6. 6. Start the BIND named service: 'systemctl start named' or 'service named start'.
  7. 7. Verify the installed version matches the fixed release: 'named -v' or 'named -V'.
  8. 8. Monitor system resources and DNS query handling to confirm the resource exhaustion vulnerability is mitigated.
Caveat No specific breaking changes mentioned in the advisory; standard version upgrade precautions apply (backup config, test in staging if possible)

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-5950 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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