Security readout for executives and security teams
Plain-English summary
CVE-2021-1504 can let an unauthenticated remote attacker crash certain Cisco ASA or FTD VPN-facing devices, causing a service outage. The impact is availability, not data theft. The highest concern is internet-facing VPN infrastructure using affected AnyConnect or WebVPN configurations.
Executive priority
Prioritize remediation for internet-facing VPN gateways because successful exploitation can interrupt remote access and security perimeter availability. Internal-only or unused VPN configurations are lower urgency, but still require confirmation against Cisco guidance.
Technical view
The vulnerability is in Cisco ASA and FTD web services VPN handling. Improper HTTPS request validation can allow a crafted request to make an affected device reload, producing denial of service. CVSS 3.1 is 8.6 with network attack vector, low complexity, no privileges, and high availability impact.
Likely exposure
Exposure is likely limited to Cisco ASA or FTD deployments with specific AnyConnect and WebVPN configurations. Internet-facing VPN portals are the main concern. The supplied source bundle does not enumerate exact software versions, affected configuration predicates, or fixed releases.
Exploitation context
The source bundle does not show CISA KEV listing or cited active exploitation. Cisco describes unauthenticated remote exploitation by crafted HTTPS request, but no public exploit status is provided here. Treat as remotely reachable outage risk rather than confirmed in-the-wild activity.
Researcher notes
Evidence supports unauthenticated remote denial of service, not confidentiality or integrity impact. CWE-787 is listed, while Cisco’s description emphasizes HTTPS input-validation failure. The bundle lacks version and patch detail, so validation should be advisory-driven and non-disruptive.
Mitigation direction
- Review Cisco advisory for affected configurations and fixed-release guidance.
- Inventory Cisco ASA and FTD devices exposing HTTPS VPN services.
- Remove or disable unnecessary AnyConnect or WebVPN exposure where operationally feasible.
- Restrict VPN web service access to required networks where feasible.
- Monitor for unexpected ASA or FTD reloads and VPN outage events.
Validation and detection
- Confirm whether ASA or FTD devices expose HTTPS VPN services.
- Compare device versions and VPN configuration against Cisco’s vulnerable-products guidance.
- Check whether AnyConnect or WebVPN features are enabled on exposed interfaces.
- Review device logs for unexpected reloads or repeated HTTPS VPN errors.
- Verify remediation status against Cisco’s advisory before closing exposure.
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-787: 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-2021-1504 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
- 20210428 Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Web Services VPN 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.
Out-of-bounds Write
Out-of-bounds Write represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.