Security readout for executives and security teams
Plain-English summary
Cisco ASA and FTD WebVPN can be tricked into adding attacker-chosen HTTP headers to responses after a user clicks a crafted link. The main business risk is user redirection or response manipulation through a VPN-facing interface, not direct device takeover. Public data here does not show active exploitation.
Executive priority
Treat as a medium-priority internet/VPN edge issue. It is not a direct remote takeover based on the supplied evidence, but VPN-facing response manipulation can support phishing and user redirection risk.
Technical view
This is a CWE-93 CRLF injection issue in Cisco ASA Software and Cisco FTD Software Clientless SSL VPN/WebVPN. It is unauthenticated and network-reachable, but requires user interaction. Successful exploitation can inject arbitrary HTTP headers into system responses and redirect users to attacker-chosen websites.
Likely exposure
Exposure is most likely where Cisco ASA or FTD Clientless SSL VPN/WebVPN is enabled and reachable by users. The source bundle does not include affected version ranges or configuration prerequisites beyond the WebVPN component.
Exploitation context
The attacker must persuade a WebVPN interface user to click a crafted link. CISA KEV is false in the supplied data, and no cited source in the bundle reports active exploitation.
Researcher notes
CVSS 3.0 is 4.7: AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N. The key constraints are required user interaction and limited integrity impact. Version-level affected data and exact fixes are not present in the source bundle.
Mitigation direction
- Review Cisco's advisory for affected releases and fixed software guidance.
- Upgrade affected ASA or FTD software according to Cisco guidance.
- Restrict WebVPN exposure where it is not business-required.
- Educate VPN users to avoid untrusted WebVPN links.
Validation and detection
- Inventory Cisco ASA and FTD assets with Clientless SSL VPN/WebVPN enabled.
- Compare running software versions against Cisco's advisory.
- Confirm WebVPN is disabled where not needed.
- Review change records for completed Cisco software updates.
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-93: Exact CWE lookup
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Open ATT&CK lookupCVE-2020-3561 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
- 4.7 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
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:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N2.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
4.7MediumVector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20201021 Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software WebVPN CRLF Injection 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.
Improper Neutralization of CRLF Sequences ('CRLF Injection')
Improper Neutralization of CRLF Sequences ('CRLF Injection') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.