Secure Firewall Threat DefenseApplication · Cisco
CVE-2021-1501
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 SIP inspection engine of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a crash and reload of an affected device, resulting in a denial of service (DoS) condition.The vulnerability is due to a crash that occurs during a hash lookup for a SIP pinhole connection. An attacker could exploit this vulnerability by sending crafted SIP traffic through an affected device. A successful exploit could allow the attacker to cause a crash and reload of the affected 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 confidenceA memory corruption vulnerability in the SIP inspection engine of Cisco ASA and FTD software allows an unauthenticated remote attacker to crash the device by sending specially crafted SIP traffic. The crash occurs during a hash lookup operation for SIP pinhole connections, likely due to improper handling of the hash table or a null pointer dereference.
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
>= 6.2.2, < 6.4.0.12>= 6.5.0, < 6.6.4>= 6.7.0, < 6.7.0.2
Adaptive Security Appliance SoftwareOperating system
>= 9.8, < 9.8.4.34>= 9.9, < 9.9.2.85>= 9.10, < 9.12.4.18>= 9.13, < 9.13.1.21>= 9.14, < 9.14.2.13>= 9.15, < 9.15.1.15CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify your Cisco device type and softwareRun 'show version' on the device CLI to determine if you are running ASA or FTD software and note the exact version numberAffected if The device is an ASA or FTD running a version within the affected ranges listed in the CVE
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Confirm the version is vulnerableCompare your installed version to these ranges - FTD: 6.2.2 to 6.4.0.11, 6.5.0 to 6.6.3, or 6.7.0 to 6.7.0.1; ASA: 9.8 to 9.8.4.33, 9.9 to 9.9.2.84, 9.10 to 9.12.4.17, 9.13 to 9.13.1.20, 9.14 to 9.14.2.12, or 9.15 to 9.15.1.14Affected if Your version falls within any of these vulnerable ranges
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Verify SIP inspection is enabledRun 'show run | include sip' or 'show running-config inspection sip' in ASA CLI; for FTD, check your inspection policy in FMC/FDM under Policies > Security Intelligence > Network Analysis or Inspect policiesAffected if SIP inspection is actively applied to traffic - the vulnerability only triggers when SIP inspection is enabled and processes the specially crafted traffic
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Check for recent device crashesReview logs and run 'show crashinfo' or 'show tech-support' for any recent reloads; look for SIP-related crash traces in the logsAffected if The device has recently crashed with symptoms pointing to SIP inspection processing
You are affected if you run a vulnerable ASA or FTD version AND have SIP inspection enabled on your device, as the flaw requires the SIP inspection engine to be active for the memory corruption to occur.
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 data6.4.0.126.6.46.7.0.2
Apply the Cisco security patch for CVE-2021-1501 by upgrading to a fixed ASA/FTD software version. If patching is immediately infeasible, consider blocking SIP traffic at upstream devices or disabling SIP inspection if not required, though this may impact legitimate VoIP communications.
Fix this in Secure Firewall Threat Defense
Scoped from the published advisory
- Consultation4.0 h
- Implementation3.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-1501 — 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-2021-1501 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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