Email Security Appliance FirmwareOperating system · Cisco
CVE-2019-1955
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 · uneditedA vulnerability in the Sender Policy Framework (SPF) functionality of Cisco AsyncOS Software for Cisco Email Security Appliances (ESA) could allow an unauthenticated, remote attacker to bypass configured user filters on the device. The vulnerability is due to incomplete input and validation checking mechanisms for certain 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. A successful exploit could allow the attacker to bypass the header filters that are configured for the affected device, which could allow malicious content 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 · moderate confidenceA vulnerability in Cisco Email Security Appliance's Sender Policy Framework (SPF) processing allows unauthenticated remote attackers to bypass configured header filters by sending specially crafted SPF packets. The issue stems from incomplete input validation of SPF messages, allowing malicious content to pass through the device without being filtered.
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
< 4.0mr1= 12.0CVSS 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
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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 checksWork through these to decide whether this CVE applies to you.
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Confirm Cisco Email Security Appliance is in useIdentify if the system is a Cisco ESA by checking the device hostname, management interface, or running 'version' command in the CLIAffected if The device is not a Cisco ESA - this CVE only applies to Cisco ESA devices
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Check AsyncOS firmware versionRun 'version' in the ESA CLI or view the version via the web interface under System Administration > Software UpgradeAffected if The installed version is lower than 4.0mr1 (for example, 3.x, 4.0) OR the version is exactly 12.0
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Verify SPF checking is enabledIn the ESA web interface, navigate to Mail Policies > SPF Verification or run 'spfconfig' in the CLI to check if SPF verification is turned onAffected if SPF verification is disabled - the bypass only affects systems actively checking SPF records
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Review SPF-related header filtersCheck existing header filters that act on SPF results via Mail Policies > Inbound Mail Policies in the web interface, or run 'filters' command in CLIAffected if Header filters rely on SPF pass/fail results to take action on messages - these can be bypassed
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Audit recent email logs for SPF anomaliesSearch mail logs for SPF-related messages using 'grep -i spf' or the ESA log subscription viewer, noting any unusual patterns of SPF-passing messages from known bad sendersAffected if Logs show SPF-passing messages that should have been flagged based on sender reputation or content analysis
The environment is affected if the AsyncOS firmware version is lower than 4.0mr1 or exactly 12.0 AND SPF verification is enabled on the appliance.
Generated from the published advisory. Verify against your own configuration.
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 data4.0mr1
Apply the relevant Cisco security updates for AsyncOS software. In the interim, review and supplement email filtering policies with additional validation layers (e.g., DMARC, DKIM checks) to compensate for SPF filter bypass.
Fix this in Email Security Appliance Firmware
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,176.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2019-1955 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2019-1955 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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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.
- 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