Security readout for executives and security teams
Plain-English summary
This flaw can let an outside attacker bypass Cisco firewall NAT inspection logic and cause unauthorized connections to an internal host. The source describes user interaction as required and impact as limited integrity only, so urgency is moderate unless exposed ASA or FTD systems protect sensitive internal services.
Executive priority
Treat as a planned remediation item, not an emergency, unless exposed firewalls protect sensitive internal hosts or browser-driven traffic paths are high risk.
Technical view
CVE-2021-34791 affects Cisco ASA and FTD Application Level Gateway behavior for NAT. Cisco describes multiple ALG bypass issues publicly discussed as NAT Slipstreaming. CVSS 3.1 is 4.7: network exploitable, low complexity, no privileges, user interaction required, changed scope, low integrity impact.
Likely exposure
Organizations using Cisco ASA or FTD with NAT ALG functionality may be exposed. The provided affected product list explicitly names Cisco ASA Software; the CVE description and Cisco advisory title also reference FTD.
Exploitation context
The bundle does not show CISA KEV listing or active exploitation evidence. It does state the issue was publicly discussed as NAT Slipstreaming. CVSS indicates exploitation requires user interaction, reducing likelihood for unattended compromise.
Researcher notes
Evidence is limited to the CVE bundle and Cisco advisory reference. Do not infer exploit availability, broader products, or specific fixes beyond Cisco’s published guidance. The weakness is categorized as CWE-358.
Mitigation direction
- Review the Cisco advisory for affected releases, fixed releases, and workarounds.
- Prioritize updates for internet-facing ASA or FTD deployments using NAT ALG.
- Reduce unnecessary ALG/NAT inspection exposure where Cisco guidance permits.
- Monitor Cisco security updates for revised remediation guidance.
Validation and detection
- Inventory Cisco ASA and FTD devices performing NAT ALG functions.
- Map device software versions against the Cisco advisory.
- Confirm whether affected features are enabled on exposed firewall paths.
- Review vulnerability scanner findings against Cisco’s official advisory scope.
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-358: 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-2021-34791 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 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/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:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N2.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.7MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20211027 Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Application Level Gateway Bypass 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.
Improperly Implemented Security Check for Standard
Improperly Implemented Security Check for Standard represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.