What is CVE-2026-21523?
Time-of-check time-of-use (toctou) race condition in GitHub Copilot and Visual Studio allows an authorized attacker to execute code over a network.
The record classifies CVE-2026-21523 under weakness class CWE-367. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs a user to take an action first, and has high impact on confidentiality, integrity, availability. 2 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 271 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 8 — HIGH
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 - EPSS (FIRST)
- 0.7% probability of exploitation in the next 30 days, higher than 54.4% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 6.2/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-02-10, last modified 2026-08-19
Is CVE-2026-21523 being exploited?
It currently carries a trending score of 19 in the Threadlinqs vulnerability feed.
Affected products and versions
- Microsoft: Visual Studio Code CoPilot Chat Extension, Visual Studio Code
How to fix CVE-2026-21523
Patch reference: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21523. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.
Threat activity tracking CVE-2026-21523
1 tracked threat in the Threadlinqs corpus references CVE-2026-21523, either in the campaign’s CVE list or as an indicator on the campaign record.
Sources
Enriched from CVE.org, FIRST EPSS. Last verified by Threadlinqs on .