CVE-2026-21521
CVE-2026-21521 is a high-severity vulnerability in Microsoft 365 Word Copilot with a CVSS 3.x base score of 7.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-150.
Key facts
- Severity: High (CVSS 3.x base score 7.4)
- EPSS exploit prediction: 1% (39th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-4498
- Weakness: CWE-150
- Affected product: Microsoft 365 Word Copilot
- Published:
- Last modified:
Description
Improper neutralization of escape, meta, or control sequences in Copilot allows an unauthorized attacker to disclose information over a network.
Frequently asked questions
- What is CVE-2026-21521?
- Improper neutralization of escape, meta, or control sequences in Copilot allows an unauthorized attacker to disclose information over a network.
- How severe is CVE-2026-21521?
- CVE-2026-21521 has a CVSS 3.x base score of 7.4, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.
- Is CVE-2026-21521 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (39th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-21521?
- CVE-2026-21521 affects Microsoft 365 Word Copilot. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-21521?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
- Does CVE-2026-21521 have an EU (EUVD) identifier?
- Yes. CVE-2026-21521 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-4498.
- When was CVE-2026-21521 published?
- CVE-2026-21521 was published on 2026-01-22 and last updated on 2026-06-17.
References
Affected products (1)
- cpe:2.3:a:microsoft:365_word_copilot:-:*:*:*:*:*:*:*
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