Security readout for executives and security teams
Plain-English summary
Hancom Office 2020 has a high-severity flaw where opening a malicious malformed document can corrupt memory and may let an attacker run code as the user. This requires user interaction, so business risk is highest where staff receive or process external documents.
Executive priority
Treat this as a targeted document-risk issue, not a network-worm scenario. Prioritize teams that handle external files, then patch or apply vendor guidance once confirmed.
Technical view
CVE-2021-21958 is a CWE-122 heap-based buffer overflow in Hancom Office 2020 11.0.0.2353, specifically Hword HwordApp.dll functionality. The CVSS 3.0 score is 7.8 with local attack vector, low complexity, no privileges required, and required user interaction.
Likely exposure
Exposure is limited to systems running Hancom Office 2020 version 11.0.0.2353. The practical exposure path is document handling, especially opening files received from email, web downloads, or external partners.
Exploitation context
The sources state a specially crafted malformed file can trigger memory corruption and potential arbitrary code execution. The CVE is not listed as KEV in the provided bundle, and no cited source here supports active exploitation.
Researcher notes
The evidence supports memory corruption and possible arbitrary code execution but does not include exploit availability, observed exploitation, or a named fixed version. Avoid assuming broader Hancom products or versions are affected beyond the listed build.
Mitigation direction
- Inventory endpoints for Hancom Office 2020 11.0.0.2353.
- Check Hancom and Talos guidance for fixed versions or vendor workarounds.
- Prioritize updating affected installations once vendor-corrected builds are confirmed.
- Limit opening Hancom documents from untrusted or unexpected sources.
- Use email and endpoint controls to flag suspicious document attachments.
Validation and detection
- Confirm installed Hancom Office versions on managed endpoints.
- Verify whether Hword and HwordApp.dll are present on exposed workstations.
- Review EDR telemetry for Hword crashes or suspicious child processes.
- Check mail and web download flows for externally sourced Hancom files.
- Document whether a vendor update or workaround has been applied.
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-122: 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-2021-21958 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
- High
- CVSS
- 7.8 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
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:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H1.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
7.8HighVector: CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://talosintelligence.com/vulnerability_reports/TALOS-2021-1386CVE reference · x_refsource_MISC
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.
Heap-based Buffer Overflow
Heap-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.