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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-2017-6627

HIGH · 7.5 CVSS v3.1 Published 2017-09-07
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
In the wild 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
A vulnerability in the UDP processing code of Cisco IOS 15.1, 15.2, and 15.4 and IOS XE 3.14 through 3.18 could allow an unauthenticated, remote attacker to cause the input queue of an affected system to hold UDP packets, causing an interface queue wedge and a denial of service (DoS) condition. The vulnerability is due to Cisco IOS Software application changes that create UDP sockets and leave the sockets idle without closing them. An attacker could exploit this vulnerability by sending UDP packets with a destination port of 0 to an affected device. A successful exploit could allow the attacker to cause UDP packets to be held in the input interfaces queue, resulting in a DoS condition. The input interface queue will stop holding UDP packets when it receives 250 packets. Cisco Bug IDs: CSCup10024, CSCva55744, CSCva95506.

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

A vulnerability in Cisco IOS and IOS XE UDP processing allows remote attackers to cause UDP packet queue buildup by sending packets to destination port 0. The flaw stems from applications creating UDP sockets that remain idle and unclosed, causing the input interface queue to wedge when receiving these packets, resulting in DoS until 250 packets are received to clear the queue.

MitigationApply Cisco software updates/patches to address the vulnerable IOS versions (15.1, 15.2, 15.4) and IOS XE versions (3.14-3.18). This is a software remediation requiring Cisco IOS/IOS XE version upgrade.

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:= 15.1\(2\)gc= 15.1\(2\)gc1= 15.1\(2\)gc2= 15.1\(4\)gc= 15.1\(4\)gc1= 15.1\(4\)gc2= 15.2\(1\)gc= 15.2\(1\)gc1= 15.2\(1\)gc2= 15.2\(2\)gc= 15.2\(3\)gc= 15.2\(3\)gc1
Ios XeOperating system
Affected:= 3.14.0s= 3.14.1s= 3.14.2s= 3.14.3s= 3.14.4s= 3.15.0s= 3.15.1cs= 3.15.1s= 3.15.2s= 3.15.3s= 3.15.4s= 3.16.0cs

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
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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. Identify the Cisco IOS or IOS XE version
    Run 'show version' on the device CLI and locate the version string in the output
    Affected if The version matches any of the listed affected versions: IOS 15.1(2)gc through 15.2(3)gc1, or IOS XE 3.14.0s through 3.16.0cs
  2. Verify network exposure to UDP port 0
    Review inbound ACLs or firewall rules on upstream devices to determine if UDP packets to destination port 0 can reach the Cisco device from untrusted networks
    Affected if UDP traffic to port 0 is permitted from external/untrusted sources
  3. Check for accumulated packets in input interface queues
    Run 'show interface' or 'show interfaces statistics' and examine input queue drops or packet accumulation, particularly on edge-facing interfaces
    Affected if There are unusual input queue drops or wedged queues without corresponding high legitimate traffic
  4. Review UDP socket usage on the device
    Use 'show udp' or 'show ip sockets' (if available) to identify open UDP sockets that remain idle for extended periods
    Affected if There are idle UDP sockets that remain open without active use

The device is affected if it runs an affected IOS/IOS XE version AND has exposure to UDP port 0 traffic from untrusted networks.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply Cisco software updates/patches to address the vulnerable IOS versions (15.1, 15.2, 15.4) and IOS XE versions (3.14-3.18). This is a software remediation requiring Cisco IOS/IOS XE version upgrade.

Recommended fix Moderate confidence

Cisco IOS XE 3.18 or later (specific fixed release varies by platform; consult Cisco advisory for exact version)

  1. 1. Identify the exact Cisco IOS or IOS XE version currently running on the affected device using 'show version' command
  2. 2. Determine if the device is running an affected version (iOS 15.1, 15.2, or 15.4; IOS XE 3.14 through 3.18)
  3. 3. Check Cisco's official security advisory for this vulnerability (CVE-2017-6627) to obtain the specific fixed release for your platform
  4. 4. Download the fixed IOS/IOS XE release from Cisco's software download center
  5. 5. Plan maintenance window as upgrade will require device reload
  6. 6. Backup current device configuration before proceeding
  7. 7. Upload the fixed IOS/IOS XE image to the device using TFTP, FTP, or USB storage
  8. 8. Configure the device to boot from the new image using 'boot system' command
Caveat IOS upgrade may require configuration review and could introduce compatibility issues with existing features or management scripts

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

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-2017-6627 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