CVE-2026-81949
HIGHCVE-2026-81949 is a high-severity (CVSS 7.8) CWE-190 vulnerability in microsoft 365 apps. O3 Security detects and blocks CVE-2026-81949 exploitation at runtime via eBPF exploit-chain detection and L7 egress monitoring, even on unpatched systems.
Integer overflow or wraparound in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-81949.
Description
Integer overflow or wraparound in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
Affected Products
365 appsmicrosoftexcelmicrosoftmicrosoft 365microsoftoffice 2016microsoftoffice 2019microsoftoffice 2021microsoftDetection & mitigation playbook
Vendor / applianceDetect
Inventory every microsoft 365 apps deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for remote code execution at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
Remediation status
No patch has shipped for CVE-2026-81949 yet — track the microsoft 365 apps advisory for a fixed release and apply the workarounds below in the meantime.
Mitigate without a patch
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2026-81949 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.
Tailored to CVE-2026-81949. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-81949 being exploited in your environment?
O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2026-81949 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.