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Nx OsOperating system · Cisco

CVE-2019-1965

HIGH · 7.7 CVSS v3.1 Published 2019-08-28
Fix available
A fix is available. Upgrade to 6.2 / 7.0 or later.
See remediation →
83/100
Remediation priority · High
Remotely reachable 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
A vulnerability in the Virtual Shell (VSH) session management for Cisco NX-OS Software could allow an authenticated, remote attacker to cause a VSH process to fail to delete upon termination. This can lead to a build-up of VSH processes that overtime can deplete system memory. When there is no system memory available, this can cause unexpected system behaviors and crashes. The vulnerability is due to the VSH process not being properly deleted when a remote management connection to the device is disconnected. An attacker could exploit this vulnerability by repeatedly performing a remote management connection to the device and terminating the connection in an unexpected manner. A successful exploit could allow the attacker to cause the VSH processes to fail to delete, which can lead to a system-wide denial of service (DoS) condition. The attacker must have valid user credentials to log in to the device using the remote management connection.

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

In Cisco NX-OS Software, the Virtual Shell (VSH) process fails to properly clean up when remote management connections (such as SSH) are terminated abruptly. Repeatedly connecting and abnormally disconnecting causes VSH processes to accumulate in memory without being deleted. Over time, this memory leak depletes available system memory, leading to system instability, unexpected behavior, and ultimately a denial of service condition.

MitigationApply the Cisco-provided software patch for CVE-2019-1965; until then, limit exposure by restricting remote management access to trusted management networks and monitor for unusual VSH process accumulation.

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
Nx OsOperating system
Affected:>= 5.2, < 6.2\(29\)>= 7.3, < 8.4>= 7.0\(3\)f, < 9.2< 7.1\(5\)n1\(1b\)>= 7.3, < 7.3\(5\)n1\(1\)< 6.2\(22\)>= 7.2, < 7.3\(4\)d1\(1\)>= 8.0, < 8.2\(3\)>= 8.3, < 8.4< 7.0\(3\)i4\(9\)>= 7.0\(3\)i7, < 7.0\(3\)i7\(4\)>= 7.0\(3\)i7, < 7.0\(3\)i7\(6\)

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
Low
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

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. Determine NX-OS software version
    Execute 'show version' on the device CLI and locate the 'NX-OS' or 'system' version line (often labeled as 'Cisco Nexus Operating System' or 'NX-OS')
    Affected if The installed version falls within any of the affected ranges: >= 5.2 and < 6.2(29); >= 7.3 and < 8.4; >= 7.0(3)f and < 9.2; < 7.1(5)n1(1b); >= 7.3 and < 7.3(5)n1(1); < 6.2(22); >= 7.2 and < 7.3(4)d1(1); >= 8.0 and < 8.2(3); >= 8.3 and < 8.4; < 7.0(3)i4(9); >= 7.0(3)i7 and < 7.0(3)i7(4); >= 7.0(3)i7
  2. Verify SSH remote management is enabled
    Execute 'show ssh' or 'show running-config | include ssh' to check if SSH server is configured for remote management access
    Affected if SSH is enabled, as the vulnerability is triggered through SSH (or similar remote management) connections being abruptly terminated
  3. Check for accumulated VSH processes
    Execute 'show process' or 'show system internal processes vsh' to list active VSH shell processes. Compare the count of VSH processes against the number of active SSH sessions using 'show ssh' or 'show sessions'
    Affected if The number of VSH processes in the process list significantly exceeds the number of active SSH management sessions, indicating leaked processes from prior terminated connections
  4. Monitor system memory utilization
    Execute 'show system resources' or 'show memory' to review available system memory
    Affected if Memory utilization is abnormally high or steadily increasing without corresponding legitimate workload, which may indicate the VSH memory leak is active

The device is affected if it runs a vulnerable NX-OS version from the listed ranges AND has SSH remote management enabled, with observable accumulation of VSH processes or depleted system memory.

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 6.2 / 7.0 / 7.1 or later
Fixed in 6.27.07.1
Interim mitigation

Apply the Cisco-provided software patch for CVE-2019-1965; until then, limit exposure by restricting remote management access to trusted management networks and monitor for unusual VSH process accumulation.

Fix this in Nx Os Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,120
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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-2019-1965 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