dbcve.org
Debian LinuxOperating system · Debian

CVE-2019-25042

CRITICAL · 9.8 CVSS v3.1 Published 2021-04-27
Fix available
A fix is available. Upgrade to 1.9.5 or later.
See remediation →
100/100
Remediation priority · Urgent
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
Unbound before 1.9.5 allows an out-of-bounds write via a compressed name in rdata_copy. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

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 · moderate confidence

Unbound DNS server before version 1.9.5 contains an out-of-bounds write vulnerability in the rdata_copy function when processing compressed names in DNS resource records. This memory corruption flaw could potentially allow remote code execution, though the vendor disputes practical exploitability.

MitigationUpgrade Unbound to version 1.9.5 or later to address the vulnerability. If immediate upgrade is not feasible, restrict network access to the DNS server as a defense-in-depth measure.

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
Debian LinuxOperating system
Affected:= 9.0
UnboundApplication
Affected:< 1.9.5

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
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 Unbound installation
    Run 'unbound -h' or 'unbound-control version' to obtain the installed version number
    Affected if The version displayed is lower than 1.9.5
  2. Check package version on Debian
    Run 'dpkg -l unbound' or 'apt show unbound' on Debian-based systems to retrieve the package version
    Affected if The installed Debian package version corresponds to an Unbound build earlier than 1.9.5
  3. Verify DNS service status
    Run 'systemctl status unbound' or check if unbound process is running to confirm the DNS server is active
    Affected if Unbound is running and the version is below 1.9.5
  4. Inspect configuration for remote access
    Check unbound.conf for 'access-control: allow' or similar settings that permit queries from untrusted networks
    Affected if Unbound is exposed to network and version is below 1.9.5

A system is affected if Unbound DNS server version is below 1.9.5 and the service is running and processing DNS 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 1.9.5 or later
Fixed in 1.9.5
Interim mitigation

Upgrade Unbound to version 1.9.5 or later to address the vulnerability. If immediate upgrade is not feasible, restrict network access to the DNS server as a defense-in-depth measure.

Recommended fix High confidence

Unbound 1.9.5 or later

  1. 1. Check the current installed version of Unbound: `unbound -V` or `unbound-control version`
  2. 2. For Debian 9.0, update the package repository: `apt update`
  3. 3. Upgrade Unbound to version 1.9.5 or later: `apt install unbound=1.9.5*` or `apt install unbound` to get latest available
  4. 4. If version 1.9.5 is not available in Debian 9 backports, consider using the official Unbound distribution from unbound.net or compile from source
  5. 5. After upgrade, restart the Unbound service: `systemctl restart unbound` or `service unbound restart`
  6. 6. Verify the installed version: `unbound -V` or `unbound-control version` to confirm version 1.9.5 or higher is running

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

Fix this in Debian Linux 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
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Scan for this in your stack

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dbcve dependency scanner

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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-2019-25042 in production — separate from our analysis above.

No notes yet

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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