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Ubuntu LinuxOperating system · Canonical

CVE-2018-5738

HIGH · 7.5 CVSS v3.0 Published 2019-01-16
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
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
Change #4777 (introduced in October 2017) introduced an unforeseen issue in releases which were issued after that date, affecting which clients are permitted to make recursive queries to a BIND nameserver. The intended (and documented) behavior is that if an operator has not specified a value for the "allow-recursion" setting, it SHOULD default to one of the following: none, if "recursion no;" is set in named.conf; a value inherited from the "allow-query-cache" or "allow-query" settings IF "recursion yes;" (the default for that setting) AND match lists are explicitly set for "allow-query-cache" or "allow-query" (see the BIND9 Administrative Reference Manual section 6.2 for more details); or the intended default of "allow-recursion {localhost; localnets;};" if "recursion yes;" is in effect and no values are explicitly set for "allow-query-cache" or "allow-query". However, because of the regression introduced by change #4777, it is possible when "recursion yes;" is in effect and no match list values are provided for "allow-query-cache" or "allow-query" for the setting of "allow-recursion" to inherit a setting of all hosts from the "allow-query" setting default, improperly permitting recursion to all clients. Affects BIND 9.9.12, 9.10.7, 9.11.3, 9.12.0->9.12.1-P2, the development release 9.13.0, and also releases 9.9.12-S1, 9.10.7-S1, 9.11.3-S1, and 9.11.3-S2 from BIND 9 Supported Preview Edition.

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

BIND 9 contains a regression (introduced in change #4777, October 2017) where the allow-recursion setting incorrectly inherits a default of 'all hosts' from allow-query when recursion yes is enabled but no explicit values are set for allow-query-cache or allow-query. This improperly permits recursive DNS queries from any client instead of the intended default restriction to localhost/localnets.

MitigationExplicitly configure the 'allow-recursion' option in named.conf to restrict recursive queries to authorized clients (e.g., 'allow-recursion { localhost; localnets; };'), or set 'recursion no;' if recursion is not required, or explicitly set allow-query-cache/allow-query to appropriate match lists.

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
Ubuntu LinuxOperating system
Affected:= 18.04
BindApplication
Affected:= 9.9.12= 9.10.7= 9.11.3= 9.12.0= 9.12.1= 9.13.0

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
High
Integrity
None
Availability
None

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

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. Check installed BIND version
    Run 'named -v' or 'named -V' to display the BIND version, or check the package manager (dpkg -l bind9 or rpm -qa bind)
    Affected if The installed version matches one of the affected versions: 9.9.12, 9.10.7, 9.11.3, 9.12.0, 9.12.1, or 9.13.0, or is Ubuntu 18.04 with packaged BIND
  2. Verify recursion is enabled
    Inspect the named.conf file (usually in /etc/bind/named.conf.options or /etc/named.conf) and look for the 'recursion' setting, or run 'rndc status' and check for recursion status
    Affected if recursion is set to 'yes' (this is the default setting)
  3. Check if allow-recursion is explicitly configured
    Search the named.conf files for 'allow-recursion' directive using 'grep -r allow-recursion /etc/bind/' or 'named-checkconf -p' to dump the configuration
    Affected if allow-recursion is NOT present or not explicitly set in the configuration
  4. Check if allow-query-cache or allow-query are explicitly configured
    Search the named.conf files for 'allow-query-cache' and 'allow-query' directives using 'grep -E "allow-query" /etc/bind/named.conf*'
    Affected if Neither allow-query-cache nor allow-query is explicitly configured in the options or view blocks

You are affected if you run an affected BIND version with recursion enabled but have not explicitly set allow-recursion AND have not explicitly set allow-query-cache or allow-query, allowing any host to perform recursive queries by default.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Explicitly configure the 'allow-recursion' option in named.conf to restrict recursive queries to authorized clients (e.g., 'allow-recursion { localhost; localnets; };'), or set 'recursion no;' if recursion is not required, or explicitly set allow-query-cache/allow-query to appropriate match lists.

Fix this in Ubuntu Linux Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
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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-2018-5738 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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