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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 24 Mar 2022.
iOSOperating system · Cisco

CVE-2017-6739

HIGH · 8.8 CVSS v3.1 Published 2017-07-17
Fix available
A fix is available. Upgrade to after 15.6 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild 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 SNMP implementation of could allow an authenticated, remote attacker to cause a reload of the affected system or to remotely execute code. An attacker could exploit this vulnerability by sending a crafted SNMP packet to the affected device.  The vulnerability is due to a buffer overflow in the affected code area. The vulnerability affects all versions of SNMP (versions 1, 2c, and 3). The attacker must know the SNMP read only community string (SNMP version 2c or earlier) or the user credentials (SNMPv3). An exploit could allow the attacker to execute arbitrary code and obtain full control of the system or to cause a reload of the affected system. Only traffic directed to the affected system can be used to exploit this vulnerability.

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

Buffer overflow vulnerability in SNMP implementation allows authenticated remote attackers to execute arbitrary code or cause system reload. Attackers need valid SNMP credentials (community string for v1/2c or user credentials for v3) and send crafted SNMP packets to the affected device.

MitigationApply vendor patches for the SNMP implementation; alternatively, restrict SNMP access to trusted IP addresses via ACLs, disable SNMP if unnecessary, or upgrade to SNMPv3 with authentication and encryption.

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
iOSOperating system
Affected:>= 12.0, <= 12.4>= 15.0, <= 15.6
Ios XeOperating system
Affected:>= 2.2.0, <= 3.17.0

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
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/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. Identify Cisco iOS version
    Run 'show version' command and locate the version string (typically in the first few lines). Compare the version number against the affected ranges: 12.0 through 12.4, or 15.0 through 15.6
    Affected if The iOS version falls within 12.0-12.4 or 15.0-15.6
  2. Identify Cisco IOS XE version
    Run 'show version' command and locate the version string. Compare the version number against the affected range: 2.2.0 through 3.17.0
    Affected if The IOS XE version falls within 2.2.0-3.17.0
  3. Verify SNMP is enabled
    Run 'show snmp' or 'show running-config | include snmp' to check if SNMP configuration exists on the device
    Affected if SNMP is enabled and configured on the device
  4. Check SNMP version in use
    Examine the SNMP configuration output for the presence of community strings (SNMPv1/v2c) or user-based security model (SNMPv3). Look for 'snmp-server community' or 'snmp-server user' entries in the configuration
    Affected if Any of SNMP versions 1, 2c, or 3 are configured and active

The device is vulnerable if it runs an affected Cisco iOS or IOS XE version AND has SNMP enabled with version 1, 2c, or 3 configured

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 15.6
Interim mitigation

Apply vendor patches for the SNMP implementation; alternatively, restrict SNMP access to trusted IP addresses via ACLs, disable SNMP if unnecessary, or upgrade to SNMPv3 with authentication and encryption.

Fix this in iOS Exploited in the wild — priority engagement
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,130
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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-2017-6739 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