Threat Intelligence / CVE / CVE-2026-21523

CVE-2026-21523 — Microsoft Visual Studio Code CoPilot Chat Extension

CVSS v3.1 8 (HIGH) · EPSS 0.0% (higher than 10.7% of all scored CVEs) · Priority 4.4/10 · Published 2026-02-10

As of 2026-05-11, CVE-2026-21523 is a HIGH-severity vulnerability in Microsoft Visual Studio Code CoPilot Chat Extension, CVSS v3.1 8, EPSS 0.0% (10.7th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-21523, most recently “CVE-2026-21523: TOCTOU Race Condition in GitHub Copilot / Visual Studio Enables Authorized Network Code Execution”.

Last updated: 2026-05-11

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 224 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)
0.0% probability of exploitation in the next 30 days, higher than 10.7% of all scored CVEs
CISA KEV
Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority
4.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published
2026-02-10, last modified 2026-05-11

Is CVE-2026-21523 being exploited?

It currently carries a trending score of 8 in the Threadlinqs vulnerability feed.

Affected products and versions

How to fix CVE-2026-21523

No vendor patch reference has been recorded for CVE-2026-21523 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

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

Seeded from cveorg and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.

Full detection coverage & IOCs for threats exploiting CVE-2026-21523 are available via the Threadlinqs MCP server (Purple tier). View plans →

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