Security readout for executives and security teams
Plain-English summary
CVE-2021-1590 affects Cisco NX-OS Software when the system login block-for feature responds to detected login attacks. A remote unauthenticated attacker could trigger repeated login process restarts, causing authentication delays. This is a denial-of-service issue, not a data theft or privilege escalation issue based on the provided sources.
Executive priority
Treat this as a moderate operational resilience issue. It can delay administrator access to network devices during login attacks, which may complicate incident response, but the provided sources do not indicate data compromise, privilege escalation, or confirmed active exploitation.
Technical view
The vulnerability is in the NX-OS system login block-for command implementation. A logic error can restart the login process when a brute-force login attack is detected and acted upon. CVSS 3.1 is 5.3, network reachable, low complexity, no privileges, no user interaction, with low availability impact.
Likely exposure
Exposure is most likely on Cisco NX-OS devices where system login block-for is configured and remote login services are reachable by untrusted networks. The bundle does not name exact affected versions or device models.
Exploitation context
The provided sources describe exploitation through a brute-force login attack against an affected device. CISA KEV status is false in the bundle, and no cited source states active exploitation or public exploit availability.
Researcher notes
The evidence is limited to the CVE data and Cisco advisory reference. The source bundle does not provide exact affected versions, fixed releases, or workaround text. The listed CWE is CWE-787, while the description characterizes the root cause as a logic error.
Mitigation direction
- Review the Cisco advisory for affected and fixed NX-OS release guidance.
- Inventory NX-OS devices using the system login block-for command.
- Restrict management login access to trusted administrative networks where feasible.
- Monitor for brute-force login activity and authentication process restarts.
- Prioritize remediation on internet-exposed or broadly reachable management interfaces.
Validation and detection
- Confirm whether Cisco NX-OS Software is present in the environment.
- Check configurations for the system login block-for command.
- Compare installed NX-OS versions against Cisco advisory guidance.
- Review authentication logs for brute-force attempts and login process restarts.
- Verify management interfaces are not exposed to untrusted networks.
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-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-2021-1590 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:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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:U/C:N/I:N/A:L3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.3MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source materials
- CVE List V5 sourceCVE List V5
- 20210825 Cisco NX-OS Software system login block-for 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.
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.