Security readout for executives and security teams
Plain-English summary
CVE-2021-40117 can let a remote, unauthenticated attacker crash affected Cisco ASA or FTD devices by abusing SSL/TLS packet handling. The business impact is service interruption: firewall, VPN, or security gateway functions may reload and become temporarily unavailable.
Executive priority
High priority for organizations using Cisco ASA or FTD at the perimeter. The issue affects availability rather than data confidentiality, but a reload of a firewall or VPN gateway can disrupt business access and security controls. Prioritize externally reachable systems first.
Technical view
The vulnerability is in the SSL/TLS message handler of Cisco ASA Software and Cisco FTD Software. Improper processing of incoming SSL/TLS packets can cause device reload. CVSS 3.1 is 8.6: network-reachable, low complexity, no privileges, no user interaction, with high availability impact only.
Likely exposure
Exposure is most likely where Cisco ASA or FTD devices accept SSL/TLS traffic from untrusted networks, including internet-facing security gateways or VPN services. The source bundle does not provide affected version ranges, so exact exposure requires checking Cisco’s advisory against deployed software versions.
Exploitation context
The provided sources describe remote unauthenticated DoS via crafted SSL/TLS packets. The CVE is not marked KEV in the bundle, and no cited source here confirms active exploitation. Treat this as a high availability risk, not confirmed exploited-in-the-wild evidence.
Researcher notes
Evidence is limited to the CVE description and Cisco advisory reference. The bundle does not include affected version ranges, fixed releases, workarounds, or exploitation telemetry. Validation should focus on product/version mapping, SSL/TLS exposure, and operational signs of unexpected reloads.
Mitigation direction
- Check Cisco’s advisory for affected releases and fixed software guidance.
- Prioritize remediation for internet-facing ASA and FTD devices.
- Restrict SSL/TLS exposure to trusted networks where operationally feasible.
- Plan maintenance windows for upgrades because affected devices may be perimeter-critical.
- Monitor Cisco guidance for any updated workaround or fixed-release details.
Validation and detection
- Inventory Cisco ASA and FTD devices in production.
- Identify devices exposing SSL/TLS services to untrusted networks.
- Compare deployed versions with Cisco’s advisory.
- Review device logs for unexpected reloads or SSL/TLS-related faults.
- Confirm monitoring alerts cover firewall and VPN device reload events.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
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Open ATT&CK lookupCVE-2021-40117 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 8.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H3.94Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.6HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20211027 Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software SSL/TLS Denial of Service VulnerabilityCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.