Security readout for executives and security teams
Plain-English summary
This flaw can make a vulnerable Cisco ASA or FTD VPN device reload, interrupting site-to-site VPN service. It is not a simple internet drive-by issue: the attacker must impersonate a trusted IKEv2 VPN peer and have valid credentials for that peer.
Executive priority
Treat as a controlled-priority availability risk. It is not reported as actively exploited here, but affected VPN gateways can support critical connectivity, so remediation should be scheduled based on business dependency and version exposure.
Technical view
CVE-2021-40125 affects Cisco ASA Software and Cisco FTD Software IKEv2 site-to-site VPN handling. Improper resource control can let an authenticated remote attacker send malformed authenticated IKEv2 messages and trigger device reload. The CVSS 3.1 score is 5.3 with high attack complexity and high availability impact.
Likely exposure
Exposure is most relevant to organizations running Cisco ASA or FTD as IKEv2 site-to-site VPN endpoints. Risk depends on affected software versions, configured trusted VPN peers, and whether valid peer credentials could be obtained or abused.
Exploitation context
The provided sources do not show CISA KEV listing or active exploitation. Exploitation requires both spoofing a trusted IKEv2 site-to-site VPN peer and possessing valid IKEv2 credentials for that peer, which materially raises the bar.
Researcher notes
The bundle identifies Cisco ASA and FTD IKEv2 site-to-site VPN processing, authenticated malformed IKEv2 messages, and device reload as the impact. Version details and fixed releases are not included in the bundle, so validation should rely on Cisco's advisory.
Mitigation direction
- Review Cisco's advisory for affected releases, fixed software, and any official workarounds.
- Inventory Cisco ASA and FTD devices providing IKEv2 site-to-site VPN service.
- Prioritize remediation for VPN gateways supporting critical business connectivity.
- Review VPN peer credential handling and rotate credentials if compromise is suspected.
Validation and detection
- Confirm whether deployed ASA or FTD versions match Cisco's affected software guidance.
- Identify devices with IKEv2 site-to-site VPN enabled and trusted peer relationships configured.
- Check operational logs for unexpected reloads around VPN negotiation activity.
- Verify remediation status against Cisco advisory guidance after maintenance.
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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CWE-416: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-40125 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
- Medium
- CVSS
- 5.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/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:H/PR:L/UI:N/S:U/C:N/I:N/A:H1.63.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.3MediumVector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/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 IKEv2 Site-to-Site VPN 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.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.