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Email Security ApplianceApplication · Cisco

CVE-2018-0447

MEDIUM · 5.3 CVSS v3.0 Published 2018-10-05
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
62/100
Remediation priority · Elevated
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 anti-spam protection mechanisms of Cisco AsyncOS Software for the Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to bypass certain content filters on an affected device. The vulnerability is due to incomplete input and validation checking mechanisms for certain Sender Policy Framework (SPF) messages that are sent to an affected device. An attacker could exploit this vulnerability by sending a customized SPF packet to an affected device. If successful, an exploit could allow the attacker to bypass the URL filters that are configured for the affected device, which could allow malicious URLs to pass through the device.

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 AsyncOS Software for the Email Security Appliance allows unauthenticated remote attackers to bypass URL filters by sending specially crafted Sender Policy Framework (SPF) packets. The flaw exists due to incomplete input and validation checking mechanisms for certain SPF messages, enabling malicious URLs to pass through the affected device.

MitigationApply the relevant Cisco security patch for CVE-2018-0447 and verify that SPF-based filtering and URL filters are functioning correctly after the update.

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
Email Security ApplianceApplication
Affected:all versions

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
Low
Availability
None

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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 the Email Security Appliance version
    Access the ESA CLI and run the 'version' or 'show version' command to display the currently installed AsyncOS version and build number
    Affected if The device is running any version of Cisco AsyncOS for Email Security Appliance - all versions are affected by this CVE
  2. Confirm SPF filtering is enabled
    Access the ESA configuration interface and verify whether SPF-based message filtering or SPF verification is turned on in the mail flow policies
    Affected if SPF filtering or SPF verification is enabled, as the vulnerability allows bypass specifically through SPF messages
  3. Verify URL filtering is configured
    Check the ESA configuration for active URL filtering policies, including URL reputation or URL-based content filters that process incoming messages
    Affected if URL filtering policies are active, since the CVE allows malicious URLs to bypass these filters via crafted SPF packets
  4. Inspect SPF policy configuration
    Review the SPF handling configuration in the ESA mail flow policies to determine how SPF pass/fail results are processed and whether they interact with URL filtering
    Affected if SPF results are configured to allow messages to pass without additional filtering, creating the condition for bypass
  5. Check for URL filtering exceptions tied to SPF
    Look for any configuration settings that may exempt or conditionally process URLs based on SPF authentication results
    Affected if SPF-based exceptions or conditional URL processing rules exist in the configuration

If the device runs any version of Cisco Email Security Appliance with SPF filtering enabled and URL filters active, it is vulnerable to CVE-2018-0447 and may be allowing malicious URLs to pass through unchecked via specially crafted SPF packets.

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

Apply the relevant Cisco security patch for CVE-2018-0447 and verify that SPF-based filtering and URL filters are functioning correctly after the update.

Fix this in Email Security Appliance Scoped from the published advisory
  • Consultation3.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,800
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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-2018-0447 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