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Debian LinuxOperating system · Debian

CVE-2007-0956

HIGH · 10.0 CVSS v2.0 Published 2007-04-06
Fix available
A fix is available. Upgrade to 1.6.1 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
The telnet daemon (telnetd) in MIT krb5 before 1.6.1 allows remote attackers to bypass authentication and gain system access via a username beginning with a '-' character, a similar issue to CVE-2007-0882.

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

The MIT krb5 telnetd daemon before version 1.6.1 contains an authentication bypass vulnerability where usernames beginning with a '-' character are not properly processed during authentication, allowing remote attackers to bypass authentication controls and gain unauthorized system access.

MitigationUpgrade to krb5 version 1.6.1 or later to patch the vulnerability, or disable the telnet service entirely and migrate to secure alternatives such as SSH.

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:= 3.1= 4.0
Ubuntu LinuxOperating system
Affected:= 5.10= 6.06= 6.10
Kerberos 5Application
Affected:< 1.6.1

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
Authentication
None
Confidentiality
Complete
Integrity
Complete
Availability
Complete

AV:N/AC:L/Au:N/C:C/I:C/A:C

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. Confirm telnet service is running
    Run 'ps aux | grep telnetd' or check if port 23 is listening with 'netstat -anp | grep :23' or 'ss -tlnp | grep :23'
    Affected if telnetd process is running or port 23 is listening, indicating the vulnerable service is active
  2. Identify krb5 telnetd binary version
    Run 'telnetd -version' or check the package version with 'dpkg -l | grep krb5' (Debian/Ubuntu) or 'rpm -qa | grep krb5' (RPM-based systems)
    Affected if The installed krb5 or telnetd version is less than 1.6.1, or the package version matches Debian 3.1/4.0, Ubuntu 5.10/6.06/6.10
  3. Verify telnet authentication configuration
    Check /etc/inetd.conf or /etc/xinetd.d/telnet for telnet service configuration, and review PAM configuration in /etc/pam.d/login or /etc/pam.d/telnet if they exist
    Affected if telnet service is configured to allow authentication (not explicitly disabled or commented out)
  4. Check for user accounts with '-' prefix
    Run 'awk -F: '($1 ~ /^-/) {print $1}' /etc/passwd' to list any system users whose names begin with a dash
    Affected if Any valid user accounts exist with usernames beginning with '-' character, which could potentially exploit this flaw

Your environment is affected if telnetd is running and the installed krb5 version is below 1.6.1, or matches the vulnerable Debian/Ubuntu releases listed.

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 1.6.1 or later
Fixed in 1.6.1
Interim mitigation

Upgrade to krb5 version 1.6.1 or later to patch the vulnerability, or disable the telnet service entirely and migrate to secure alternatives such as SSH.

Recommended fix High confidence

MIT krb5 >= 1.6.1

  1. Identify the MIT krb5 telnetd package installed on the system
  2. Upgrade krb5 to version 1.6.1 or later using the system's package manager (e.g., apt-get update && apt-get install krb5 or apt-get upgrade krb5)
  3. After upgrading, restart the telnetd service or reboot the system to apply changes
  4. Verify the new krb5 version is installed: dpkg -l | grep krb5 or krb5-config --version
  5. Alternatively, consider disabling the telnet service entirely and using SSH (secure shell) as a more secure remote access method
Caveat Minor: Ensure any Kerberos-dependent services are compatible with the new version before production deployment

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
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
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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-2007-0956 in production — separate from our analysis above.

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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