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Debian LinuxOperating system · Debian

CVE-2015-5296

MEDIUM · 5.4 CVSS v3.1 Published 2015-12-29
Fix available
A fix is available. Upgrade to 4.1.22 / 4.2.7 or later.
See remediation →
63/100
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
Samba 3.x and 4.x before 4.1.22, 4.2.x before 4.2.7, and 4.3.x before 4.3.3 supports connections that are encrypted but unsigned, which allows man-in-the-middle attackers to conduct encrypted-to-unencrypted downgrade attacks by modifying the client-server data stream, related to clidfs.c, libsmb_server.c, and smbXcli_base.c.

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

Samba versions 3.x and 4.x before 4.1.22, 4.2.7, and 4.3.3 support SMB connections that are encrypted but unsigned, allowing man-in-the-middle attackers to modify the client-server data stream and downgrade encrypted connections to unencrypted ones, exposing sensitive data.

MitigationUpgrade Samba to a patched version (4.1.22+, 4.2.7+, or 4.3.3+) or configure SMB signing requirements to prevent downgrade 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
Debian LinuxOperating system
Affected:= 7.0= 8.0
Ubuntu LinuxOperating system
Affected:= 12.04= 14.04= 15.04= 15.10
SambaApplication
Affected:>= 3.2.0, < 4.1.22>= 4.2.0, < 4.2.7>= 4.3.0, < 4.3.3

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
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/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 Samba version
    Run 'smbd --version' or 'samba --version' to get the exact version number. On Debian/Ubuntu, also run 'dpkg -l | grep samba' to list installed Samba packages.
    Affected if The version falls within: >= 3.2.0 and < 4.1.22, OR >= 4.2.0 and < 4.2.7, OR >= 4.3.0 and < 4.3.3
  2. Locate Samba configuration file
    The main configuration is typically at /etc/samba/smb.conf. Verify its location using 'testparm -s' which will show the loaded configuration path.
    Affected if Configuration file exists and Samba service is running
  3. Check for SMB encryption settings
    Search the smb.conf for 'smb encrypt' or 'encrypt passwords' directives. Run 'testparm -v 2>/dev/null | grep -i encrypt' to list encryption-related parameters.
    Affected if 'smb encrypt' is set to 'auto' or 'desired' (values that enable encryption without requiring signing)
  4. Check SMB signing configuration
    Run 'testparm -v 2>/dev/null | grep -i sign' to see 'server signing' and 'client signing' settings. Also examine smb.conf directly for these parameters.
    Affected if 'server signing' is not set to 'mandatory' or 'required', allowing unsigned encrypted connections
  5. Verify running smbd process
    Run 'ps aux | grep smbd' or 'pgrep -a smbd' to confirm the Samba daemon is actively running and using the checked configuration.
    Affected if Samba daemon is running with an affected version and vulnerable configuration

You are affected if running an affected Samba version (3.2.0 to 4.1.21, 4.2.0 to 4.2.6, or 4.3.0 to 4.3.2) with SMB encryption enabled but SMB signing not set to mandatory.

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 4.1.22 / 4.2.7 / 4.3.3 or later
Fixed in 4.1.224.2.74.3.3
Interim mitigation

Upgrade Samba to a patched version (4.1.22+, 4.2.7+, or 4.3.3+) or configure SMB signing requirements to prevent downgrade attacks.

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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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-2015-5296 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