How severe is CVE-2026-42831?

CVE-2026-42831 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-42831 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-42831?

CVE-2026-42831 primarily affects Microsoft 365 Copilot. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-42831?

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-2026-42831 have an EU (EUVD) identifier?

Yes. CVE-2026-42831 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29711.

When was CVE-2026-42831 published?

CVE-2026-42831 was published on 2026-05-12 and last updated on 2026-06-17.

CVE-2026-42831

CVE-2026-42831 is a high-severity vulnerability in Microsoft 365 Copilot with a CVSS 3.x base score of 7.8. 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-122.

Key facts

Severity: High (CVSS 3.x base score 7.8)
EPSS exploit prediction: 0% (35th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-29711
Weakness: CWE-122
Affected product: Microsoft 365 Copilot
Published: 2026-05-12
Last modified: 2026-06-17

Description

Heap-based buffer overflow in Microsoft Office allows an unauthorized attacker to execute code locally.

Frequently asked questions

What is CVE-2026-42831?: Heap-based buffer overflow in Microsoft Office allows an unauthorized attacker to execute code locally.
How severe is CVE-2026-42831?: CVE-2026-42831 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-42831 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-42831?: CVE-2026-42831 primarily affects Microsoft 365 Copilot. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-42831?: 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-2026-42831 have an EU (EUVD) identifier?: Yes. CVE-2026-42831 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29711.
When was CVE-2026-42831 published?: CVE-2026-42831 was published on 2026-05-12 and last updated on 2026-06-17.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42831

Affected products (3)

cpe:2.3:a:microsoft:365_copilot:*:*:*:*:*:android:*:*
cpe:2.3:a:microsoft:office:2024:*:*:*:ltsc:macos:*:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:macos:*:*

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