Patch Tuesday, February 2026 Edition

Improper neutralization of special elements used in a command ('command injection') in GitHub Copilot and Visual Studio allows an unauthorized attacker to execute code over a network.

CVE-2026-21509 is a security feature bypass in Microsoft Office caused by reliance on untrusted input when making a security decision (CWE-807): Office trusts attacker-controlled data when deciding whether a protection applies, allowing an unauthorized local attacker to bypass that security feature. Exploitation is local and requires user interaction (per the CVSS vector), most plausibly by getting a user to open a crafted file or document, and the flaw carries high confidentiality, integrity, and availability impact. Anyone running Microsoft Office, Microsoft 365 Apps, or Office Long Term Servicing Channel is in scope, giving the flaw a potential audience in the hundreds of millions of seats. The flaw is being actively exploited: it was added to CISA's Known Exploited Vulnerabilities catalog on 2026-01-26, Microsoft issued an emergency patch, and headlines attribute in-the-wild use to Russian state hackers targeting Ukrainian and EU organizations, including the maritime and transport sectors (a related APT28 campaign was tied to a separate Office/MSHTML 0-day, CVE-2026-21513). EPSS estimates a 72.6% probability of exploitation within the next 30 days (99th percentile).

Do: Apply Microsoft's emergency Office update and the follow-on February 2026 Patch Tuesday fixes across Microsoft 365 Apps, Office, and Office LTSC, checking Microsoft's advisory for the exact affected builds since no version ranges are given in the source data. Given the KEV listing, federal agencies must patch per CISA BOD 22-01 timelines (or follow cloud-service guidance). Hunt for exploitation per vendor guidance — headlines report Russian state use against EU/Ukrainian and maritime/transport targets — and prioritize endpoints where users open untrusted files.

Microsoft Windows Shell contains a protection mechanism failure (CWE-693) that allows an unauthorized attacker to bypass a security feature, which CISA notes can be reached over a network. Successful exploitation defeats a Windows defense-in-depth control, weakening protections an attacker would otherwise have to evade as part of a broader intrusion; the available data does not describe a code-execution or privilege-escalation gain. Any system running Microsoft Windows falls within CISA's published affected scope, and specific version ranges have not been enumerated in the available data. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2026-02-10, confirming exploitation in the wild, and its EPSS score of 26.2% (98th percentile) signals elevated near-term exploitation risk; ransomware use is unknown and no public proof-of-concept is known.

Do: Apply Microsoft's applicable Windows security update through Windows Update/WSUS or your patch-management process as soon as practical, prioritizing internet-exposed and high-value systems; because the issue is in CISA's KEV catalog (added 2026-02-10), U.S. federal agencies must apply the vendor fix, applicable BOD 22-01 mitigations (including for cloud services), or discontinue use by the catalog due date. Until patched, follow Microsoft's mitigation guidance from vendor advisories and monitor for updates, since specific affected builds and the exploited security feature have not been detailed in the available data.

CVE-2026-21514 is a security feature bypass in Microsoft Word caused by the application relying on untrusted inputs when making a security decision (CWE-807). The flaw carries a local attack vector with a user-interaction requirement, so it is most plausibly triggered when a user opens attacker-supplied content, such as a crafted document, on a system running Word. A local, unauthorized attacker who exploits it can circumvent a Word security feature, with high-impact confidentiality, integrity, and availability effects on the local system; bypasses of this type are commonly chained with other flaws for deeper compromise. Any organization running Microsoft 365 Apps or Office Long Term Servicing Channel (LTSC) is affected. CISA added the bug to the Known Exploited Vulnerabilities catalog on 2026-02-10, confirming exploitation in the wild, though no public proof-of-concept is known and EPSS currently estimates a 1.5% chance of exploitation in the next 30 days (73rd percentile).

Do: Apply the February 2026 Patch Tuesday security updates from Microsoft for Microsoft 365 Apps and Office LTSC immediately; fixed version numbers were not provided in the source data, so use Microsoft's release guidance to confirm builds. Because the flaw is in CISA KEV, federal agencies must satisfy BOD 22-01 by applying the update (or directed mitigations) within the mandated weeks, and all organizations should prioritize endpoints that open untrusted documents. Until patched, consider Office hardening such as marking files from the internet as untrusted in Word and watching for anomalous document-driven local activity.

Improper neutralization of special elements used in a command ('command injection') in Github Copilot allows an unauthorized attacker to execute code over a network.

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.