CVE-2026-21523
TOCTOU race in GitHub Copilot and Visual Studio enables remote code execution.
Is CVE-2026-21523 being exploited?
Not confirmed. CVE-2026-21523 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.81% probability of exploitation in the next 30 days.
How severe is CVE-2026-21523?
CVE-2026-21523 is rated High with a CVSS score of 8.0. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-21523?
Yes. A fix has been recorded for CVE-2026-21523. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-21523 affect?
CVE-2026-21523 affects GitHub Copilot, Microsoft Visual Studio. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-21523?
Monitor vendor advisories; restrict tool access; apply patch when released
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution via network by an authorized attacker exploiting TOCTOU in IDE tooling.
Patch when available
- affected>= 0.27.0 and < 0.37.1
- affected>= 1.0.0 and < 1.110.1
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.