dbcve.org
Ios XrOperating system · Cisco

CVE-2019-1686

HIGH · 8.6 CVSS v3.1 Published 2019-04-17
Fix available
A fix is available. Upgrade to 6.5.2 / 6.6.1 or later.
See remediation →
95/100
Remediation priority · Urgent
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 TCP flags inspection feature for access control lists (ACLs) on Cisco ASR 9000 Series Aggregation Services Routers could allow an unauthenticated, remote attacker to bypass protection offered by a configured ACL on an affected device. The vulnerability is due to incorrect processing of the ACL applied to an interface of an affected device when Cisco Express Forwarding load balancing using the 3-tuple hash algorithm is enabled. An attacker could exploit this vulnerability by sending traffic through an affected device that should otherwise be denied by the configured ACL. An exploit could allow the attacker to bypass protection offered by a configured ACL on the affected device. There are workarounds that address this vulnerability. Affected Cisco IOS XR versions are: Cisco IOS XR Software Release 5.1.1 and later till first fixed. First Fixed Releases: 6.5.2 and later, 6.6.1 and later.

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 the TCP flags inspection for ACLs on Cisco ASR 9000 Series Routers allows unauthenticated remote attackers to bypass configured ACLs. The flaw is due to incorrect ACL processing when Cisco Express Forwarding (CEF) load balancing uses the 3-tuple hash algorithm, causing traffic that should be denied to be permitted.

MitigationApply the fixed IOS XR releases (6.5.2+, 6.6.1+) or implement workarounds such as disabling the 3-tuple hash algorithm for CEF load balancing if upgrading is not immediately feasible.

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
Ios XrOperating system
Affected:>= 5.1.1, < 6.5.2>= 6.5.3, < 6.6.1

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
Changed
Confidentiality
None
Integrity
High
Availability
None

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

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 device model
    Run 'show platform' or 'show version' to confirm the device is a Cisco ASR 9000 Series Router
    Affected if Device is not an ASR 9000 series router - the vulnerability does not apply
  2. Check IOS XR version
    Run 'show version' and locate the IOS XR release number
    Affected if Version is within 5.1.1 to 6.5.1, or 6.5.3 to 6.6.0 - these ranges are vulnerable
  3. Verify CEF is enabled
    Run 'show cef interface' or 'show ip cef' to check if Cisco Express Forwarding is active
    Affected if CEF is disabled - the 3-tuple hash algorithm condition does not apply
  4. Check CEF load-balancing algorithm
    Run 'show cef load-balancing' to see which hash algorithm is configured for CEF load balancing
    Affected if Output shows '3-tuple' hash algorithm is in use - this is the vulnerable configuration
  5. Confirm TCP flag-based ACLs exist
    Run 'show access-lists' and review ACL entries for 'tcp-flags' or 'established' keywords that inspect TCP flags
    Affected if No ACLs with TCP flag inspection are configured - the bypass cannot be exploited on non-TCP-flag ACLs

The device is affected if it is an ASR 9000 running a vulnerable IOS XR version (5.1.1-6.5.1 or 6.5.3-6.6.0), has CEF enabled with the 3-tuple hash algorithm, and has ACLs that inspect TCP flags.

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 6.5.2 / 6.6.1 or later
Fixed in 6.5.26.6.1
Interim mitigation

Apply the fixed IOS XR releases (6.5.2+, 6.6.1+) or implement workarounds such as disabling the 3-tuple hash algorithm for CEF load balancing if upgrading is not immediately feasible.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
30.0 hours of engineering $5,280
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $8,448.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2019-1686 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2019-1686 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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