Security readout for executives and security teams
Plain-English summary
This is a Fortinet appliance vulnerability where a privileged local user could crash or take over affected software by abusing the TFTP client handling. It is not described as remotely exploitable, but compromise of an administrator or local account could turn this into full device compromise.
Executive priority
Treat as a scheduled but firm remediation item. It is not currently evidenced as actively exploited, but affected security appliances are high-value control points and successful exploitation could compromise confidentiality, integrity, and availability.
Technical view
CVE-2021-42757 is a stack buffer overflow in the TFTP client library, mapped to CWE-121/CWE-120. The CVSS 3.1 vector is 6.3 with local attack vector, low complexity, high privileges required, no user interaction, unchanged scope, and high confidentiality, integrity, and availability impact.
Likely exposure
Most exposure is in Fortinet environments running affected FortiOS versions, especially before 6.4.7 or 7.0.0 through 7.0.2. The bundle also lists other Fortinet products and versions, so asset owners should verify against Fortinet advisory data before scoping remediation.
Exploitation context
The supplied sources do not show CISA KEV listing or confirmed active exploitation. Exploitation requires authenticated local access with high privileges and crafted command line arguments, making this more likely as a post-compromise or insider-abuse risk than an internet-scale entry point.
Researcher notes
The key uncertainty is product scope beyond FortiOS because the description centers on FortiOS while the source bundle lists multiple Fortinet products. Use the Fortinet advisory as the authoritative reference for affected versions, fixed releases, and product-specific guidance.
Mitigation direction
- Upgrade affected FortiOS systems per Fortinet advisory FG-IR-21-173.
- Check Fortinet guidance for listed non-FortiOS products before assuming exposure.
- Restrict local CLI and administrative access to trusted operators only.
- Review privileged account usage and remove unnecessary administrator access.
Validation and detection
- Inventory Fortinet products and firmware versions across the environment.
- Identify FortiOS systems before 6.4.7 or 7.0.0 through 7.0.2.
- Compare listed assets with Fortinet advisory FG-IR-21-173.
- Review logs for unusual privileged local CLI activity.
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-120: 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 lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-42757 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
- 6.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H/E:P/RL:U/RC:C
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:H/I:H/A:H/E:P/RL:U/RC:C0.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.3MediumVector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H/E:P/RL:U/RC:C
Source materials
- CVE List V5 sourceCVE List V5
- https://fortiguard.com/advisory/FG-IR-21-173CVE reference
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.
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.