Secure Firewall Threat DefenseApplication · Cisco
CVE-2021-1495
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 · uneditedMultiple Cisco products are affected by a vulnerability in the Snort detection engine that could allow an unauthenticated, remote attacker to bypass a configured file policy for HTTP. The vulnerability is due to incorrect handling of specific HTTP header parameters. An attacker could exploit this vulnerability by sending crafted HTTP packets through an affected device. A successful exploit could allow the attacker to bypass a configured file policy for HTTP packets and deliver a malicious payload.
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 confidenceThis vulnerability in Cisco's Snort detection engine allows remote attackers to bypass configured HTTP file policies by sending crafted HTTP packets with specific malformed header parameters. The Snort engine incorrectly processes these headers, permitting malicious payloads to pass through without being blocked by the file inspection policy.
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
Secure Firewall Threat DefenseApplication
< 6.4.0.12>= 6.5.0, < 6.6.4>= 6.7.0, < 6.7.0.2
Ios XeApplication
>= 16.12, < 16.12.5>= 17.1, < 17.3.3>= 17.4, < 17.4.1< 2.9.17.1CVSS 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:3.1/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 checksWork through these to decide whether this CVE applies to you.
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Identify the installed product and versionRun 'show version' on the Cisco device or check the Snort version via 'snort --version'Affected if The version falls within: FTD < 6.4.0.12, FTD 6.5.0-6.6.3, FTD 6.7.0-6.7.0.1; IOS Xe 16.12.x before 16.12.5, 17.1.x-17.3.2, 17.4.x before 17.4.1; or Snort versions before 2.9.17.1
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Confirm Snort is actively inspecting HTTP trafficCheck the device configuration for enabled Snort inspection on HTTP ports, typically via 'show service-policy' or examining the inspection policy mapAffected if Snort inspection is enabled for HTTP traffic (ports 80, 8080, etc.)
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Verify HTTP file policy is configuredExamine the HTTP file inspection policy via 'show policy-map' or the device management interface to see if file policies are definedAffected if An HTTP file policy exists and is applied to traffic inspection - the bypass only matters when file policies are in use
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Check for recent Snort HTTP inspection eventsReview Snort alerts and logs for HTTP traffic, particularly files being transferred - look for any unexpected allow actions on suspicious filesAffected if HTTP file transfers are being processed but not blocked despite potentially malicious file types being detected
A defender is affected if they run any of the listed product versions AND have HTTP file policies enabled with Snort inspection active, allowing crafted HTTP header packets to bypass file type restrictions.
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 data2.9.17.16.4.0.126.6.4
Apply Cisco-provided patches and updates for affected products. Ensure HTTP file policies are reviewed and consider additional inspection layers until patches are deployed.
Fix this in Secure Firewall Threat Defense
Scoped from the published advisory
- Consultation4.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,544.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-1495 — 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-2021-1495 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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- Version or environment caveats, and links to real fixes
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