Security readout for executives and security teams
Plain-English summary
CVE-2021-40118 can let an unauthenticated remote attacker crash affected Cisco ASA or FTD devices through malformed HTTPS traffic to the web services interface. The business impact is availability: firewall or threat defense reloads can interrupt VPN, perimeter security, or network access.
Executive priority
Treat as high priority where ASA or FTD web services are reachable from untrusted networks. The issue threatens availability of security infrastructure, but the provided sources do not show data theft, integrity impact, or confirmed active exploitation.
Technical view
The flaw is improper input validation while parsing HTTPS requests in Cisco ASA Software and Cisco FTD Software web services. Cisco rates it high, CVSS 3.1 score 8.6, with network access, low complexity, no privileges, and high availability impact. The bundle maps CWE-121 but does not provide affected version ranges.
Likely exposure
Organizations running Cisco ASA or FTD with the affected web services interface reachable over HTTPS are the likely exposure group. The source bundle does not specify versions or configuration prerequisites beyond affected ASA/FTD software and HTTPS request parsing.
Exploitation context
The source bundle states an unauthenticated remote attacker could send a malicious HTTPS request causing device reload and DoS. It does not cite active exploitation, and KEV status is false, so active exploitation should not be assumed from these sources.
Researcher notes
Evidence is limited to CVE metadata and Cisco’s referenced advisory. The bundle lacks version ranges, patch release details, workaround text, and proof-of-exploitation indicators. Validate exposure against Cisco’s advisory rather than inferring affected versions from product names alone.
Mitigation direction
- Review Cisco advisory for affected releases, fixed software, and any vendor workarounds.
- Prioritize updates for internet-facing or externally reachable ASA and FTD web services.
- Reduce HTTPS web services exposure to trusted networks where operationally feasible.
- Monitor for unexpected ASA or FTD reloads until remediation is complete.
Validation and detection
- Inventory Cisco ASA and FTD assets exposing HTTPS web services.
- Compare running software releases against Cisco advisory guidance.
- Check device logs for unexpected reloads or crash events linked to HTTPS handling.
- Confirm remediation by documenting upgraded versions or vendor-approved mitigations.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-121: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-40118 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
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 Web Services Denial of Service VulnerabilitiesCVE 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.
Stack-based Buffer Overflow
Stack-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.