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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-2017-6740

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
The Simple Network Management Protocol (SNMP) subsystem of Cisco IOS and IOS XE Software contains multiple vulnerabilities that could allow an authenticated, remote attacker to remotely execute code on an affected system or cause an affected system to reload. An attacker could exploit these vulnerabilities by sending a crafted SNMP packet to an affected system via IPv4 or IPv6. Only traffic directed to an affected system can be used to exploit these vulnerabilities. The vulnerabilities are due to a buffer overflow condition in the SNMP subsystem of the affected software. The vulnerabilities affect all versions of SNMP - Versions 1, 2c, and 3. To exploit these vulnerabilities via SNMP Version 2c or earlier, the attacker must know the SNMP read-only community string for the affected system. To exploit these vulnerabilities via SNMP Version 3, the attacker must have user credentials for the affected system. A successful exploit could allow the attacker to execute arbitrary code and obtain full control of the affected system or cause the affected system to reload. Customers are advised to apply the workaround as contained in the Workarounds section below. Fixed software information is available via the Cisco IOS Software Checker. All devices that have enabled SNMP and have not explicitly excluded the affected MIBs or OIDs should be considered vulnerable. There are workarounds that address these vulnerabilities.

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 vulnerabilities in the SNMP subsystem of Cisco IOS and IOS XE Software allow an authenticated remote attacker to send crafted SNMP packets (IPv4/IPv6) that trigger the overflow, potentially enabling arbitrary code execution with full system control or causing the affected system to reload. The vulnerabilities affect SNMP versions 1, 2c, and 3, requiring either knowledge of the read-only community string (v1/v2c) or valid user credentials (v3).

MitigationApply Cisco-provided workarounds (such as disabling SNMP, restricting SNMP access via ACLs, or excluding affected MIBs/OIDs) and/or upgrade to the fixed Cisco IOS/IOS XE software version using the Cisco IOS Software Checker.

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

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. Verify SNMP is enabled on the device
    Run 'show snmp' or 'show snmp community' to check if SNMP is configured and active
    Affected if SNMP is enabled and running - the vulnerability only affects the SNMP subsystem when it is active
  2. Check installed Cisco IOS version
    Run 'show version' and locate the software version string (e.g., 15.2(4)E5)
    Affected if Version falls within 12.0-12.4, 15.0-15.6 for IOS, or 2.2.0-3.17 for IOS XE
  3. Identify SNMP configuration type
    Run 'show run | include snmp' to see SNMP configuration lines, check for 'snmp-server community' or 'snmp-server group' entries
    Affected if SNMP v1/v2c community strings or SNMPv3 user credentials are configured - exploitation requires these authentication details
  4. Check SNMP access control lists
    Run 'show ip access-lists' and review any ACLs applied to SNMP (snmp-server community XXXX ACL <num>)
    Affected if SNMP is exposed to unauthenticated or untrusted network segments - the ACL does not restrict to trusted sources only

A device is affected if it runs a vulnerable IOS/IOS XE version (12.0-12.4, 15.0-15.6 for IOS or 2.2.0-3.17 for IOS XE), has SNMP enabled, and has SNMP community strings or SNMPv3 credentials configured that could be obtained by an attacker.

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 Cisco-provided workarounds (such as disabling SNMP, restricting SNMP access via ACLs, or excluding affected MIBs/OIDs) and/or upgrade to the fixed Cisco IOS/IOS XE software version using the Cisco IOS Software Checker.

Fix this in iOS Exploited in the wild — priority engagement
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2017-6740 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