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Email Security Appliance FirmwareOperating system · Cisco

CVE-2018-15453

HIGH · 8.6 CVSS v3.1 Published 2019-01-10
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
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 Secure/Multipurpose Internet Mail Extensions (S/MIME) Decryption and Verification or S/MIME Public Key Harvesting features of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to cause an affected device to corrupt system memory. A successful exploit could cause the filtering process to unexpectedly reload, resulting in a denial of service (DoS) condition on the device. The vulnerability is due to improper input validation of S/MIME-signed emails. An attacker could exploit this vulnerability by sending a malicious S/MIME-signed email through a targeted device. If Decryption and Verification or Public Key Harvesting is configured, the filtering process could crash due to memory corruption and restart, resulting in a DoS condition. The software could then resume processing the same S/MIME-signed email, causing the filtering process to crash and restart again. A successful exploit could allow the attacker to cause a permanent DoS condition. This vulnerability may require manual intervention to recover the ESA.

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 memory corruption vulnerability in Cisco Email Security Appliance's S/MIME handling allows unauthenticated remote attackers to crash the filtering process by sending specially crafted S/MIME-signed emails. The improper input validation causes memory corruption leading to process restart loops and potential permanent DoS.

MitigationApply Cisco's patch for CVE-2018-15453 when available. As a workaround, disable S/MIME Decryption/Verification and Public Key Harvesting features if not required.

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 Appliance FirmwareOperating system
Affected:= 11.0.1-401= 11.1.0-131

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
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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 installed ESA firmware version
    Log into the Cisco Email Security Appliance CLI and run the 'version' command, or access the GUI under System Administration > Software Updates to view the current firmware build
    Affected if The version shown is exactly 11.0.1-401 or 11.1.0-131
  2. Confirm S/MIME Decryption/Verification feature is enabled
    Access the ESA GUI, navigate to Incoming Mail Policies > S/MIME Decryption and Verification settings, or use the CLI command 'smimeconfig' to view the current configuration
    Affected if S/MIME Decryption and Verification is turned ON (the feature is active)
  3. Confirm Public Key Harvesting is enabled
    Access the ESA GUI under Incoming Mail Policies > S/MIME > Public Key Harvesting settings, or check via CLI with the appropriate smime configuration commands
    Affected if Public Key Harvesting is enabled (the feature is active)

The environment is affected if the ESA firmware is exactly version 11.0.1-401 or 11.1.0-131 AND S/MIME Decryption/Verification or Public Key Harvesting features are enabled, making the device vulnerable to the memory corruption flaw via crafted S/MIME-signed emails.

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 Cisco's patch for CVE-2018-15453 when available. As a workaround, disable S/MIME Decryption/Verification and Public Key Harvesting features if not required.

Fix this in Email Security Appliance Firmware Scoped from the published advisory
  • Consultation8.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
32.0 hours of engineering $5,680
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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-2018-15453 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