# Outlook zero-click NTLM hash leak used by Russian state hackers (CVE-2023-23397) · pwn.watch

> A crafted Outlook reminder with a UNC path made Outlook for Windows send the user's NTLM hash to an attacker's server without any click. Microsoft said a Russia-based actor (APT28) used it against European government, transport, energy and military targets.

Page: https://pwn.watch/i/microsoft-outlook-ntlm-leak-cve-2023-23397 · generated 2026-10-22T23:52:53.443Z

## Status
- Severity: critical · status: closed · patch: patched
- Product: Microsoft Outlook for Windows
- Started: 2023-03-14 · closed: 2023-03-24
- CVEs: CVE-2023-23397
- Affected: See vendor advisory
- Fixed in: See vendor advisory (March 2023 security updates)

## Follow this incident
- RSS (one item per update): https://pwn.watch/i/microsoft-outlook-ntlm-leak-cve-2023-23397/feed.xml
- JSON Feed: https://pwn.watch/i/microsoft-outlook-ntlm-leak-cve-2023-23397/feed.json
- Full data (timeline, sources, posts, agentBrief): https://pwn.watch/i/microsoft-outlook-ntlm-leak-cve-2023-23397.json
- This file: https://pwn.watch/i/microsoft-outlook-ntlm-leak-cve-2023-23397/llms.txt

## Updates (newest first)
- 2023-03-24: Microsoft publishes investigation guidance for CVE-2023-23397 (https://www.microsoft.com/en-us/security/blog/2023/03/24/guidance-for-investigating-attacks-using-cve-2023-23397/)
- 2023-03-14: Patch Tuesday fix; CISA adds CVE-2023-23397 to KEV (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-23397)

## Fix brief
# Security brief: Outlook zero-click NTLM hash leak used by Russian state hackers (CVE-2023-23397)

Source: https://pwn.watch/i/microsoft-outlook-ntlm-leak-cve-2023-23397 · status: closed (closed Mar 24, 2023) · severity: critical · updated Mar 24, 2023

## Patch status
**PATCHED: fixed releases exist. Upgrade to a fixed version.**

## What it is
A crafted Outlook reminder with a UNC path made Outlook for Windows send the user's NTLM hash to an attacker's server without any click. Microsoft said a Russia-based actor (APT28) used it against European government, transport, energy and military targets.

Severity detail: CVSS 9.8 (NVD), zero-click, zero-day, actively exploited (CISA KEV)

- Product: Microsoft Outlook for Windows
- CVE / advisory ids: CVE-2023-23397

## Affected versions
- See vendor advisory

## Check whether you're affected
No generic command applies (the product is a hosted service, appliance or desktop app). Check the installed version in its admin UI / About screen and compare with the versions above.

## Fix
Upgrade to one of these fixed versions (or later on the same branch):
- See vendor advisory (March 2023 security updates)

After upgrading, re-run the checks above and redeploy/restart the affected services.

## Latest updates
- Mar 24, 2023: Microsoft publishes investigation guidance for CVE-2023-23397
- Mar 14, 2023: Patch Tuesday fix; CISA adds CVE-2023-23397 to KEV

## Advisories
- [CVE-2023-23397 Microsoft Outlook Elevation of Privilege Vulnerability](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-23397) (Microsoft)
- [Microsoft Mitigates Outlook Elevation of Privilege Vulnerability](https://msrc.microsoft.com/blog/2023/03/microsoft-mitigates-outlook-elevation-of-privilege-vulnerability/) (Microsoft)
- [NVD: CVE-2023-23397](https://nvd.nist.gov/vuln/detail/CVE-2023-23397) (NVD)
- [CISA Known Exploited Vulnerabilities Catalog](https://www.cisa.gov/known-exploited-vulnerabilities-catalog) (CISA)

## Write-ups & news
- [Guidance for investigating attacks using CVE-2023-23397](https://www.microsoft.com/en-us/security/blog/2023/03/24/guidance-for-investigating-attacks-using-cve-2023-23397/)

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Machine-readable: https://pwn.watch/i/microsoft-outlook-ntlm-leak-cve-2023-23397.json · all incidents: https://pwn.watch/incidents.json. Verify against the vendor advisory before changing production systems.