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Enterprise LinuxOperating system · Redhat

CVE-2016-0739

MEDIUM · 5.9 CVSS v3.0 Published 2016-04-13
Fix available
A fix is available. Upgrade to after 0.7.2 or later.
See remediation →
68/100
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
libssh before 0.7.3 improperly truncates ephemeral secrets generated for the (1) diffie-hellman-group1 and (2) diffie-hellman-group14 key exchange methods to 128 bits, which makes it easier for man-in-the-middle attackers to decrypt or intercept SSH sessions via unspecified vectors, aka a "bits/bytes confusion bug."

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

libssh before 0.7.3 contains a bits/bytes confusion bug in the Diffie-Hellman group1 and group14 key exchange implementations. The library improperly truncates ephemeral secrets to 128 bits instead of the intended full length, significantly weakening the key exchange and enabling MITM attackers to more easily decrypt or intercept SSH sessions.

MitigationUpgrade libssh to version 0.7.3 or later where the secret truncation has been corrected. If immediate patching is not feasible, audit SSH traffic and consider network-level protections against man-in-the-middle attacks.

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
Enterprise LinuxOperating system
Affected:= 7.0
Ubuntu LinuxOperating system
Affected:= 12.04= 14.04= 15.10
FedoraOperating system
Affected:= 22= 23
Debian LinuxOperating system
Affected:= 7.0= 8.0
LibsshApplication
Affected:<= 0.7.2

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
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.0/AV:N/AC:H/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. Identify installed libssh version
    Run 'dpkg -l libssh-4' (Debian/Ubuntu) or 'rpm -q libssh' (RHEL/Fedora) to see the installed package version. Alternatively, check the shared library version with 'ldconfig -p | grep libssh' and examine the file version, or use 'ssh -V' if your ssh client links against libssh.
    Affected if The version is 0.7.2 or lower, or the package version matches the affected OS versions (RHEL 7.0, Ubuntu 12.04/14.04/15.10, Fedora 22/23, Debian 7.0/8.0)
  2. Determine if libssh is in use
    Identify processes or applications that link against libssh by running 'ldd $(which ssh)' or 'ldconfig -p | grep libssh'. Check any custom SSH implementations or automation tools that may embed libssh.
    Affected if Any application or service is linked against a vulnerable libssh version (0.7.2 or earlier)
  3. Inspect SSH server configuration for key exchange methods
    Check SSH server config files (typically /etc/ssh/sshd_config) for the 'KexAlgorithms' or 'KeyExchanges' directive. Look for 'diffie-hellman-group1-sha1' or 'diffie-hellman-group14-sha1' which correspond to the vulnerable DH group1 and group14 implementations.
    Affected if The server configuration enables diffie-hellman-group1-sha1 or diffie-hellman-group14-sha1 key exchange algorithms while using a vulnerable libssh version

You are affected if libssh version 0.7.2 or earlier is installed and any service or client uses Diffie-Hellman group1 or group14 key exchange, as the ephemeral secrets are truncated to 128 bits.

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 0.7.2
Interim mitigation

Upgrade libssh to version 0.7.3 or later where the secret truncation has been corrected. If immediate patching is not feasible, audit SSH traffic and consider network-level protections against man-in-the-middle attacks.

Fix this in Enterprise Linux Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,540
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Scan for this in your stack

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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-2016-0739 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