Security readout for executives and security teams
Plain-English summary
CVE-2021-34761 affects Cisco Firepower Threat Defense Software. A logged-in administrator could abuse a CLI input validation flaw to overwrite or append data to system files with root-level privileges. This is not described as remotely exploitable without credentials, but it can matter on security appliances because file integrity changes may weaken controls.
Executive priority
Treat this as a moderate operational risk, highest where FTD devices protect critical networks or admin access is broadly shared. The priority is version confirmation, vendor-guided remediation, and stronger administrative access controls.
Technical view
Cisco describes incomplete input validation in a specific FTD CLI command. An authenticated local attacker with administrative privileges can supply crafted parameters and write arbitrary data to system files as root. The CVSS 3.1 score is 4.4, with high integrity impact and no confidentiality or availability impact listed.
Likely exposure
Exposure is limited to Cisco Firepower Threat Defense Software deployments where an attacker has administrative credentials and local CLI access. The source bundle does not identify exact affected versions, CPEs, or deployment-specific exposure.
Exploitation context
The provided sources do not show CISA KEV listing or active exploitation. Exploitation requires valid administrative access, so the main risk is malicious, compromised, or overprivileged administrators altering system files on an FTD device.
Researcher notes
The bundle gives the weakness class as CWE-73 and the impact as root-level arbitrary file write after administrative authentication. Exact vulnerable versions, fixed releases, and workarounds are not included in the supplied data, so Cisco’s advisory is the controlling source for remediation specifics.
Mitigation direction
- Check Cisco’s advisory for affected versions and fixed FTD releases.
- Upgrade confirmed vulnerable FTD deployments according to Cisco guidance.
- Restrict administrative CLI access to trusted management networks.
- Review administrator accounts, MFA, AAA, and least-privilege controls.
- Monitor security appliance file integrity and configuration changes.
Validation and detection
- Inventory Cisco FTD deployments and software versions.
- Compare each deployment against Cisco’s advisory applicability details.
- Review who has administrative CLI access to each device.
- Check logs for unexpected administrative CLI activity or file changes.
- Confirm patch status through change records or device management tooling.
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-73: File access and web shell behavior lookup
File traversal and upload weaknesses can lead teams to review file, web shell, execution, and collection telemetry. 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 lookupFile access behavior lookup
The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-34761 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
- 4.4 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/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:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N0.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.4MediumVector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20211027 Cisco Firepower Threat Defense Software CLI Arbitrary File Write 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.
External Control of File Name or Path
External Control of File Name or Path represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.