Is CVE-2023-23397 (Microsoft Office Outlook Privilege Escalation) being exploited in the wild?

Yes. CISA added CVE-2023-23397 to its Known Exploited Vulnerabilities catalogue on 14 March 2023, which it does only when there is reliable evidence of active exploitation. CISA has not linked it to known ransomware campaigns. Microsoft Office Outlook contains a privilege escalation vulnerability that allows for a NTLM Relay attack against another service to authenticate as the user.

What “exploited in the wild” means for CVE-2023-23397

This is not a theoretical Outlook flaw. For practitioners, the key question is whether the vulnerability is still being leveraged against exposed mailboxes or whether it is only relevant for historical patching. A KEV listing answers that operationally: treat the issue as active exploitation exposure until proven otherwise, and prioritise it ahead of ordinary backlog work.

When a vulnerability is in CISA’s Known Exploited Vulnerabilities catalogue, it is already past the “watch list” stage. The practical implication is that exposure should be assumed to exist anywhere Outlook is present, especially where Windows authentication flows and internal services may accept relayed NTLM authentication.

How this Outlook flaw creates security exposure

CVE-2023-23397 matters because the vulnerability is in Microsoft Office Outlook and enables privilege escalation through an NTLM relay path to another service. That means the problem is not confined to a single desktop application, it can become an access path into adjacent systems when a user opens crafted content and the environment still accepts the authentication flow being abused.

In operational terms, the most important question is not just whether Outlook is patched, but whether the surrounding environment still allows relay-style authentication, exposed mailboxes, or service paths that can be reached from a compromised user context. CISA Known Exploited Vulnerabilities Catalog is the authoritative place to confirm the KEV status and remediation expectations for this CVE, while the vendor advisory remains the source of truth for product-specific mitigation details.

What to check before declaring the issue closed

Because this vulnerability was exploited in the wild, closure should include more than a patch install. Teams should verify whether Outlook endpoints were reachable during the exposure window, whether mailboxes handled untrusted invitations or messages that could have triggered the flaw, and whether any downstream service shows signs of authentication abuse consistent with relay behaviour.

Where there is any doubt, the review should extend to related accounts and sessions that may have been used after compromise. If an attacker could authenticate as a user to another service, then credentials, active sessions, and any service accounts touched by that trust path may need review, rotation, or revocation depending on blast radius.

Risk and Threat Considerations

This CVE is risky because exploitation can turn a mail client weakness into broader privilege abuse. The practical danger is not just local impact on Outlook, but unauthorized access to a second service through relayed authentication, which can move the incident from endpoint exposure into account compromise or lateral access.

Failure mechanism: A crafted Outlook-triggered action can cause NTLM authentication material to be relayed to another service that trusts it, allowing an attacker to act as the user in that downstream system.

Impact: The result can be unauthorized access, privilege escalation, and follow-on compromise of other internal services or accounts reachable through that trust relationship.

Standards & Framework Alignment

This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.

NIST CSF 2.0, NIST SP 800-53 Rev 5 and CIS Controls v8 set the governance and control requirements practitioners need to meet.

Framework	Control / Reference	Relevance
NIST CSF 2.0	DE.CM-09 — Detect events	Active exploitation requires monitoring for suspicious authentication and compromise signals.
	RS.AN-01 — Analysis of Events	This CVE needs investigation of suspicious logons and possible downstream compromise.
Recommendation — Monitor authentication and endpoint events for indicators of relay abuse and follow-on compromise. Analyze suspicious logon activity and authentication patterns for evidence of exploitation.
NIST SP 800-53 Rev 5	SI-2 — Flaw Remediation	The question centers on an exploited vulnerability that demands prompt remediation.
	AU-6 — Audit Record Review, Analysis, and Reporting	Investigation depends on reviewing logs for abnormal authentication and access.
Recommendation — Remediate the Outlook vulnerability and verify deployment across exposed systems. Review authentication and access logs for suspicious activity tied to the CVE.
CIS Controls v8	CIS-7 — Continuous Vulnerability Management	KEV-listed exploitation makes prioritised vulnerability management central.
Recommendation — Prioritize and track remediation for KEV-listed vulnerabilities on exposed endpoints.

Practitioner Guidance

What to prioritise: Treat KEV-listed exploitation as a response trigger, not a routine patch queue item. Confirm whether any Outlook installation was exposed during the active exploitation period and whether the affected user population had access to services that accept Windows authentication.

What to verify: Check for signs of downstream authentication misuse, not just Outlook crashes or mail anomalies. If you find evidence of suspicious logons, unexpected relay-prone service access, or related account activity, escalate as a probable compromise investigation rather than a simple patching task.

Decision rule: If patching or configuration changes must wait, reduce exposure at the trust boundary first by limiting the affected client population, constraining risky authentication paths, and increasing monitoring around authentication events that could indicate relay abuse.

Practitioner takeaway: For exploited-mail-client CVEs, remediation is only complete when the patch, the authentication path, and the compromise check all line up; otherwise you may have removed the vulnerability but not the access path.