dbcve.org
FedoraOperating system · Fedoraproject

CVE-2023-4236

HIGH · 7.5 CVSS v3.1 Published 2023-09-20
Fix available
A fix is available. Upgrade to 9.18.18 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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
A flaw in the networking code handling DNS-over-TLS queries may cause `named` to terminate unexpectedly due to an assertion failure. This happens when internal data structures are incorrectly reused under significant DNS-over-TLS query load. This issue affects BIND 9 versions 9.18.0 through 9.18.18 and 9.18.11-S1 through 9.18.18-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 · high confidence

A flaw in BIND 9's DNS-over-TLS query handling causes the named server to terminate unexpectedly due to an assertion failure. This occurs when internal data structures are incorrectly reused under significant DNS-over-TLS query load, leading to denial of service.

MitigationUpgrade BIND 9 to version 9.18.19 or later; as a temporary workaround, consider disabling DNS-over-TLS or implementing rate limiting on DoT queries.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

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
FedoraOperating system
Affected:= 37= 38= 39
Debian LinuxOperating system
Affected:= 10.0= 11.0
BindApplication
Affected:>= 9.18.0, < 9.18.18= 9.18.11= 9.18.18
H300s FirmwareOperating system
Affected:all versions
H500s FirmwareOperating system
Affected:all versions
H700s FirmwareOperating system
Affected:all versions
H410s FirmwareOperating system
Affected:all versions
H410c FirmwareOperating system
Affected:all versions

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
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify BIND version
    Run 'named -v' or check the package manager (e.g., 'rpm -q bind' on Fedora/RHEL, 'dpkg -l bind9' on Debian) to determine the installed BIND version
    Affected if The version is 9.18.0 through 9.18.17, or specifically 9.18.11 or 9.18.18, or the version is unknown but falls within the 9.18.x branch before 9.18.19
  2. Confirm DNS-over-TLS is enabled
    Examine BIND configuration files (commonly /etc/named.conf or /etc/bind/named.conf.options) for 'dns-over-tls' or 'tls' statements, or check if port 853 is in use with 'netstat -tuln | grep 853' or 'ss -tuln | grep 853'
    Affected if DNS-over-TLS is explicitly configured and the server is listening on port 853 for DoT queries
  3. Verify DoT query load
    Monitor DNS query traffic on port 853 over time using tools like 'tcpdump -i any port 853' or review DNS query logs for DoT activity
    Affected if The server is receiving significant DNS-over-TLS query traffic, as the assertion failure occurs under high DoT load

A user is affected if they are running a vulnerable BIND 9 version (9.18.0-9.18.17 or 9.18.18) with DNS-over-TLS enabled and actively processing DoT queries.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 9.18.18 or later
Fixed in 9.18.18
Interim mitigation

Upgrade BIND 9 to version 9.18.19 or later; as a temporary workaround, consider disabling DNS-over-TLS or implementing rate limiting on DoT queries.

Recommended fix Moderate confidence

BIND 9.18.19 or later (or the latest stable 9.18.x/9.20.x release)

  1. 1. Identify the current BIND (named) version by running `named -v` or `rpm -q bind`
  2. 2. For BIND 9.18.0 through 9.18.18, upgrade to BIND 9.18.19 or later
  3. 3. On Fedora systems, run `sudo dnf update bind` or `sudo dnf update bind-chroot` to apply the fix
  4. 4. On Debian systems, run `sudo apt update && sudo apt install bind9` to obtain the fixed version
  5. 5. After upgrading, restart the named service using `sudo systemctl restart named`
  6. 6. Verify the fix is applied by checking the new version with `named -v`
  7. 7. Test DNS-over-TLS functionality to ensure normal operation
Caveat Minor: Upgrading BIND may introduce changes in behavior or configuration requirements; review release notes for 9.18.19+ before deploying in production

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

Fix this in Fedora Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,720
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,752.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2023-4236 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2023-4236 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data