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Debian LinuxOperating system · Debian

CVE-2018-15599

MEDIUM · 5.3 CVSS v3.0 Published 2018-08-21
Fix available
A fix is available. Upgrade to after 2018.76 or later.
See remediation →
62/100
Remediation priority · Elevated
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
The recv_msg_userauth_request function in svr-auth.c in Dropbear through 2018.76 is prone to a user enumeration vulnerability because username validity affects how fields in SSH_MSG_USERAUTH messages are handled, a similar issue to CVE-2018-15473 in an unrelated codebase.

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

Dropbear SSH server through version 2018.76 contains a user enumeration vulnerability in the recv_msg_userauth_request function in svr-auth.c. The vulnerability allows remote attackers to determine whether specific usernames exist on the system by observing differences in how the server processes SSH_MSG_USERAUTH messages for valid versus invalid usernames. This is caused by the server handling fields in the authentication message differently based on username validity.

MitigationUpgrade Dropbear to a patched version beyond 2018.76. Consider implementing rate limiting on authentication attempts andObscuring server responses to reduce enumeration effectiveness as defense-in-depth measures.

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:= 8.0
Dropbear SshApplication
Affected:<= 2018.76

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
Low
Integrity
None
Availability
None

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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. Identify Dropbear SSH installation
    Run 'dropbear -v' or 'dropbear --version' to check the installed binary version
    Affected if The command returns a version number of Dropbear
  2. Confirm affected version
    Compare the installed Dropbear version to the affected range: versions 2018.76 and earlier are vulnerable. Check the exact version string returned by the version command
    Affected if The installed version is 2018.76 or earlier, or the version cannot be determined (implies older/unpatched build)
  3. Check if Dropbear SSH service is running and exposed
    Run 'ps aux | grep dropbear' to see if the Dropbear daemon is active, then check network configuration (e.g., 'netstat -tlnp' or 'ss -tlnp') to verify port 22 (or custom SSH port) is listening on an external interface
    Affected if Dropbear is running and SSH port is accessible from network (not bound to 127.0.0.1 only)
  4. Verify authentication methods enabled
    Inspect Dropbear configuration (typically /etc/default/dropbear or /etc/dropbear/dropbear_config) for options like '-w' (disable password login) or '-s' (disable password authentication). Also check for '-j' (disable compression) and '-z' (disable zlib) which are unrelated but indicate configuration completeness
    Affected if Password-based authentication (-s flag not set) or keyboard-interactive authentication is enabled, allowing the enumeration attack surface

You are affected if Dropbear SSH version 2018.76 or earlier is installed, the SSH service is network-accessible, and password/keyboard-interactive authentication methods are enabled, allowing remote attackers to enumerate valid usernames.

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
Upgrade available Upgrade to a release after 2018.76
Interim mitigation

Upgrade Dropbear to a patched version beyond 2018.76. Consider implementing rate limiting on authentication attempts andObscuring server responses to reduce enumeration effectiveness as defense-in-depth measures.

Fix this in Debian 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-2018-15599 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