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Elastic Services ControllerApplication · Cisco

CVE-2021-1312

HIGH · 7.5 CVSS v3.1 Published 2021-01-20
Fix available
A fix is available. Upgrade to after 5.3.0.94 or later.
See remediation →
84/100
Remediation priority · High
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 system resource management of Cisco Elastic Services Controller (ESC) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) to the health monitor API on an affected device. The vulnerability is due to inadequate provisioning of kernel parameters for the maximum number of TCP connections and SYN backlog. An attacker could exploit this vulnerability by sending a flood of crafted TCP packets to an affected device. A successful exploit could allow the attacker to block TCP listening ports that are used by the health monitor API. This vulnerability only affects customers who use the health monitor API.

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

This vulnerability in Cisco Elastic Services Controller stems from improperly configured kernel parameters controlling maximum TCP connections and SYN backlog size. An unauthenticated remote attacker can flood the device with crafted TCP packets, exhausting resources and blocking the TCP listening ports used by the health monitor API, resulting in denial of service.

MitigationProperly configure kernel parameters for TCP connection limits and SYN backlog (e.g., tune net.ipv4.tcp_max_syn_backlog, net.core.somaxconn) and consider implementing rate limiting or SYN cookies at the network perimeter to mitigate TCP flood attacks.

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
Elastic Services ControllerApplication
Affected:<= 5.3.0.94

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 Cisco Elastic Services Controller installation
    Run 'dpkg -l | grep elastic-services-controller' or 'rpm -qa | grep elastic-services-controller' on Linux systems. Alternatively, check for running processes with 'ps aux | grep -i elastic' or look for the ESC service file in /etc/systemd/system/.
    Affected if The product is not installed or the command returns no results, indicating ESC is not present.
  2. Determine installed version of Cisco ESC
    If installed, check the version using 'escadm version' or look in /opt/cisco/esc/esc_version. Compare the version number to the affected range: any version <= 5.3.0.94 is vulnerable.
    Affected if The installed version is 5.3.0.94 or any earlier version.
  3. Verify kernel parameter net.ipv4.tcp_max_syn_backlog
    Execute 'sysctl net.ipv4.tcp_max_syn_backlog' or 'cat /proc/sys/net/ipv4/tcp_max_syn_backlog'. This controls the maximum number of connections in the SYN queue.
    Affected if The value is set to 0, a very low value (below 256), or not explicitly configured (default may be insufficient).
  4. Verify kernel parameter net.core.somaxconn
    Execute 'sysctl net.core.somaxconn' or 'cat /proc/sys/net/core/somaxconn'. This limits the maximum number of connections accepted by a single listening socket.
    Affected if The value is set to 0 or is set to an unusually low value (below 64).
  5. Confirm health monitor API accessibility
    Identify listening ports used by the health monitor API - typically check with 'netstat -tulpn | grep -E "(8080|8443|443|80)"' or review ESC configuration files in /opt/cisco/esc/esc_conf/. Verify these ports accept external TCP connections.
    Affected if The health monitor API ports are exposed to untrusted networks without additional protections.

A system is affected if Cisco Elastic Services Controller version 5.3.0.94 or lower is installed AND the kernel parameters tcp_max_syn_backlog or somaxconn are set to low or default values that do not protect against TCP SYN flood exhaustion.

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 5.3.0.94
Interim mitigation

Properly configure kernel parameters for TCP connection limits and SYN backlog (e.g., tune net.ipv4.tcp_max_syn_backlog, net.core.somaxconn) and consider implementing rate limiting or SYN cookies at the network perimeter to mitigate TCP flood attacks.

Fix this in Elastic Services Controller Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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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-2021-1312 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
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  • Version or environment caveats, and links to real fixes
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