Security readout for executives and security teams
Plain-English summary
A race condition in GitHub Copilot and Visual Studio Code can let an already authorized, low-privilege attacker execute code remotely after user interaction. Successful exploitation could compromise data, alter systems, or disrupt availability. The supplied record rates it high severity at CVSS 8.0.
Executive priority
Treat as a high-priority developer-endpoint issue. Establish exposure promptly and deploy Microsoft's official remediation. Escalate systems used for sensitive source code, credentials, production administration, or untrusted projects because successful exploitation could cause full confidentiality, integrity, and availability impact.
Technical view
CVE-2026-21523 is a CWE-367 time-of-check/time-of-use race condition. The CVSS vector indicates network reachability, low attack complexity, low privileges, required user interaction, unchanged scope, and high confidentiality, integrity, and availability impact.
Likely exposure
The supplied affected entries identify Microsoft Visual Studio Code Copilot Chat Extension 0.27.0 and Visual Studio Code 1.0.0. Exposure outside those exact entries cannot be established from the bundle. Inventory extension and editor versions, prioritizing systems that process untrusted remote content or projects.
Exploitation context
The record requires an authorized attacker and user interaction. It does not establish anonymous exploitation. KEV is false, and the supplied CVSS exploit-maturity metric is unproven. Therefore, active exploitation is not supported by the provided evidence.
Researcher notes
The bundle confirms CWE-367 and the CVSS characteristics but provides no race window, vulnerable component flow, fixed-version details, indicators of compromise, or proof of exploitation. Avoid assuming broader affected releases. Use the Microsoft advisory for current version boundaries and remediation details.
Mitigation direction
- Review the Microsoft advisory and apply its official update or remediation guidance.
- Prioritize affected developer workstations handling untrusted repositories, files, prompts, or remote content.
- Restrict unnecessary access by low-privilege or external users until remediation is confirmed.
- If immediate updating is impossible, consider disabling the affected extension after operational review.
Validation and detection
- Inventory Visual Studio Code and Copilot Chat extension versions across managed endpoints.
- Compare detected versions with the Microsoft advisory's current affected and fixed-version information.
- Confirm updates are deployed and affected versions are no longer present.
- Review endpoint telemetry for unexpected child processes or code execution associated with affected applications.
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-367: 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-2026-21523 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
- 8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/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.
SSVC decision data
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:L/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C2.15.9microsoftVulnerability scoring details
Base CVSS 3.1 score
8HighVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- GitHub Copilot and Visual Studio Code Remote Code Execution VulnerabilityCVE reference, microsoft · vendor-advisory, patch
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.
Time-of-check Time-of-use (TOCTOU) Race Condition
Time-of-check Time-of-use (TOCTOU) Race Condition represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.