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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-2017-6738

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

Multiple buffer overflow vulnerabilities in Cisco IOS/IOS XE SNMP subsystem allow authenticated remote attackers to execute arbitrary code or cause system reload via crafted SNMP packets. Affected systems include all SNMP versions (1, 2c, 3), with exploitation requiring either the SNMP community string (v1/v2c) or user credentials (v3).

MitigationApply Cisco software updates from the IOS Software Checker or implement workarounds such as excluding affected MIBs/OIDs and restricting SNMP access to trusted management networks.

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 the IOS/IOS XE version
    Execute 'show version' or 'show version | include Version' on the device CLI
    Affected if The displayed version falls within 12.0-12.4, 15.0-15.6 for IOS, or 2.2.0-3.17.0 for IOS XE
  2. Confirm SNMP is running
    Execute 'show snmp' and look for engine ID or community strings, or use 'show snmp group' to list configured groups
    Affected if SNMP is enabled and any community string or user is configured (v1/v2c shows communities, v3 shows users)
  3. Check SNMP version configuration
    Execute 'show snmp community' to list community strings, and 'show snmp user' to list SNMPv3 users
    Affected if Any SNMPv1, v2c community string, or SNMPv3 user is configured - the vulnerability affects all three versions when authenticated
  4. Verify SNMP view or MIB access
    Execute 'show snmp view' to see which views are defined and what OID trees are accessible to SNMP clients
    Affected if Any SNMP view exists that allows access to OIDs - the flaw is in the SNMP packet parsing regardless of specific OID accessed

The environment is affected if the device runs a vulnerable IOS (12.0-12.4 or 15.0-15.6) or IOS XE (2.2.0-3.17.0) version AND has any SNMP version (v1, v2c, or v3) enabled with active credentials 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.

dbcve · scoped
Upgrade available Upgrade to a release after 15.6
Interim mitigation

Apply Cisco software updates from the IOS Software Checker or implement workarounds such as excluding affected MIBs/OIDs and restricting SNMP access to trusted management networks.

Recommended fix High confidence

iOS 12.5 or later (12.x train); iOS 15.7 or later (15.x train); IOS XE 3.18 or later (3.x train) - verify via Cisco IOS Software Checker

  1. 1. Identify the current Cisco IOS or IOS XE version on the affected device using 'show version' command
  2. 2. Access the Cisco IOS Software Checker at tools.cisco.com to confirm the specific fixed release for your device's current version and train
  3. 3. If an immediate upgrade is not feasible, apply the Cisco workaround: disable SNMP or restrict SNMP access by using ACLs (access lists) to limit which IP addresses can send SNMP packets to the device
  4. 4. To apply an SNMP access list workaround, enter configuration mode and create an ACL that permits only trusted management IPs: 'ip access-list extended SNMP_ACL' followed by 'permit ip <trusted_ip> any' and 'deny ip any any'
  5. 5. Apply the ACL to SNMP by using 'snmp-server community <community_string> ro SNMP_ACL' for SNMPv2c, or for SNMPv3 apply to the group via 'snmp-server group <group_name> v3 auth read <read_view> access SNMP_ACL'
  6. 6. If upgrading, download the fixed IOS/IOS XE version from Cisco Software Download center
  7. 7. Upgrade the device using standard Cisco IOS upgrade procedures (e.g., 'archive download-sw' or 'install' command depending on platform)
  8. 8. After upgrade, verify SNMP is working correctly and the version matches a fixed release
Caveat Review Cisco release notes for your specific version upgrade; some older hardware may have limited upgrade path; ensure SNMP configurations are backed up before upgrade

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in iOS Exploited in the wild — priority engagement
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
30.0 hours of engineering $5,280
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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-2017-6738 in production — separate from our analysis above.

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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