Security readout for executives and security teams
Plain-English summary
Cisco IOS XE firewalls using Zone-Based Policy Firewall can mishandle certain UDP and ICMP traffic when UTD or AppQoE is enabled. This may let traffic pass into firewall handling incorrectly, causing drops or misleading high-speed logging figures. The business risk is policy enforcement and monitoring reliability, not data theft or service outage in the provided record.
Executive priority
Treat this as a targeted network control reliability issue. It is not rated critical, but affected perimeter firewalls may make incorrect enforcement or monitoring decisions. Prioritize validation where Cisco IOS XE ZBFW, UTD, or AppQoE protect important network boundaries.
Technical view
CVE-2021-1625 is a remote, unauthenticated Cisco IOS XE ZBFW classification issue. ICMP and UDP responder-to-initiator flows are not inspected when ZBFW is configured with Unified Threat Defense or Application Quality of Experience. CVSS 3.1 is 5.8, with network attack vector, low complexity, no privileges, changed scope, and low integrity impact.
Likely exposure
Exposure is likely limited to Cisco IOS XE deployments using Zone-Based Policy Firewall with UTD or AppQoE configured. The source bundle does not provide affected version ranges, so teams must validate device configuration and compare software releases against Cisco guidance.
Exploitation context
The CVE record describes remote exploitation by sending UDP or ICMP flows through the network. Successful exploitation can cause incorrect classification, dropped traffic, or inaccurate HSL reporting. CISA KEV status is false, and the provided sources do not support active exploitation claims.
Researcher notes
The reported weakness maps to CWE-284 and centers on missing inspection for specific ICMP and UDP flow direction handling. The source bundle does not include affected release ranges, proof-of-concept evidence, or detailed remediation text beyond the Cisco advisory reference.
Mitigation direction
- Review Cisco advisory for affected and fixed IOS XE releases.
- Apply Cisco-published fixed software or workarounds when confirmed.
- Prioritize perimeter IOS XE devices using ZBFW with UTD or AppQoE.
- Monitor Cisco guidance for advisory updates or clarifications.
Validation and detection
- Inventory Cisco IOS XE devices running Zone-Based Policy Firewall.
- Check whether UTD or AppQoE is configured with ZBFW.
- Compare device software versions against Cisco advisory guidance.
- Review logs for unexpected UDP or ICMP classification anomalies.
- Confirm HSL reporting accuracy for relevant firewall traffic flows.
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-284: Authorization and privilege behavior lookup
Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. 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-2021-1625 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
- 5.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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:N/S:C/C:N/I:L/A:N3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.8MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20210922 Cisco IOS XE Software Zone-Based Policy Firewall ICMP and UDP Inspection 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 Access Control
Improper Access Control represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.