CVE-2007-2243
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 · uneditedOpenSSH 4.6 and earlier, when ChallengeResponseAuthentication is enabled, allows remote attackers to determine the existence of user accounts by attempting to authenticate via S/KEY, which displays a different response if the user account exists, a similar issue to CVE-2001-1483.
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 confidenceOpenSSH 4.6 and earlier with ChallengeResponseAuthentication enabled reveals whether user accounts exist by responding differently to S/KEY authentication attempts for valid versus invalid usernames, enabling remote user enumeration.
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= 1.2= 1.2.1= 1.2.2= 1.2.3= 1.2.27= 2.1= 2.1.1= 2.2= 2.3= 2.5= 2.5.1= 2.5.2CVSS 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
- Authentication
- None
- Confidentiality
- Partial
- Integrity
- None
- Availability
- None
AV:N/AC:L/Au:N/C:P/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 checksWork through these to decide whether this CVE applies to you.
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Check OpenSSH server versionRun `sshd -V` or `sshd -v` to display the version, or check via package manager (dpkg -l openssh-server, rpm -q openssh-server)Affected if Version is 4.6 or earlier (such as 4.5, 4.4, etc.)
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Locate sshd_config fileThe configuration is typically at /etc/ssh/sshd_config or /etc/sshd_config. Check your system defaults with `sshd -t -f /path/to/sshd_config` to verify which config file is in useAffected if Cannot determine config location or multiple sshd configs exist with inconsistent settings
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Check if ChallengeResponseAuthentication is enabledGrep for 'ChallengeResponseAuthentication' in your sshd_config file using `grep -i ChallengeResponseAuthentication /etc/ssh/sshd_config`Affected if Directive is set to 'yes' or 'on' (or uncommented with any positive value)
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Verify S/Key authentication method availabilityCheck if the system has S/Key or OPIE installed (look for /etc/skeypwd, /etc/opiekeys, or run `which skey` or `which opieinfo`) and is configured for challenge-responseAffected if S/Key or OPIE authentication is installed and ChallengeResponseAuthentication is enabled in sshd_config
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Test authentication response differenceAttempt SSH login with a known-valid username using S/Key authentication, then with an invalid username, and compare the error messages - the timing and content may differ based on username validityAffected if Responses differ between valid and invalid usernames when ChallengeResponseAuthentication is used
You are affected if OpenSSH version is 4.6 or earlier AND ChallengeResponseAuthentication is enabled in sshd_config, allowing an attacker to enumerate valid usernames via S/Key authentication probe responses.
Generated from the published advisory. Verify against your own configuration.
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 dataDisable ChallengeResponseAuthentication in sshd_config unless required, or ensure consistent authentication responses regardless of account validity to prevent user enumeration.
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2007-2243 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2007-2243 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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