CVE-2023-23397
CVE-2023-23397 is a security flaw in Microsoft Office, part of Microsoft Office. Someone who already has a foothold can use Microsoft Office to take full control of the machine. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 14 Mar 2023.[1]
Microsoft Office is in things households have, such as phones, computers, browsers and everyday apps, so the fix matters at home as much as at work. Fixed in version https://aka.ms/OfficeSecurityReleases, 16.0.5387.1000 and 15.0.5537.1000.
Description
CISA calls it an outlook privilege escalation in Microsoft Office. In its words: “Microsoft Office Outlook contains a privilege escalation vulnerability that allows for a NTLM Relay attack against another service to authenticate as the user.”[1]
The underlying weakness is capture-replay (CWE-294), in MITRE’s list of common software weaknesses.[2]
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| Microsoft Office LTSC 2021 | https://aka.ms/OfficeSecurityReleases |
| Microsoft Outlook 2016 | 16.0.5387.1000 |
| Microsoft 365 Apps for Enterprise | https://aka.ms/OfficeSecurityReleases |
| Microsoft Office 2019 | https://aka.ms/OfficeSecurityReleases |
| Microsoft Outlook 2013 Service Pack 1 | 15.0.5537.1000 |
Every device with Microsoft Office needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 14 Mar 2023, within a day of it being made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 4 Apr 2023 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 97%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Microsoft has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Update Microsoft Office now.On Windows: Settings, Windows Update, Check for updates, then restart. Office updates come the same way, or from any Office app: File, Account, Update Options. Then turn on automatic updates, so the next fix arrives on its own.
- Check you’re on https://aka.ms/OfficeSecurityReleases or later.Fixed in version https://aka.ms/OfficeSecurityReleases, 16.0.5387.1000 and 15.0.5537.1000. Anything older is what attackers are going after.
- If there’s no update, stop using it.CISA’s advice when a flaw being used in attacks has no fix is to stop using the product until it does.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 97%.[4] |
See also
Other Microsoft Office flaws
- CVE-2009-0238: remote code execution ·
- CVE-2026-21514: word reliance on untrusted inputs in a security decision ·
- CVE-2026-21509: security feature bypass ·
- CVE-2009-0556: powerPoint code injection ·
- CVE-2007-0671: excel remote code execution ·
- CVE-2023-21715: publisher security feature bypass ·
Other Microsoft flaws
- CVE-2026-96951, Microsoft Windows: command injection ·
- CVE-2026-65660, Microsoft SharePoint: code injection ·
- CVE-2026-85880, Microsoft Windows: heap-based buffer overflow ·
- CVE-2026-81963, Microsoft Windows: link following ·
- CVE-2019-1068, Microsoft SQL Server: remote code execution ·
Added the same day
- CVE-2023-24880, Microsoft Windows: smartScreen security feature bypass ·
- CVE-2022-41328, Fortinet FortiOS: path traversal ·
Every Microsoft flaw on CISA’s list · Everything added in March 2023
References
- ^ Cybersecurity and Infrastructure Security Agency. “Microsoft Office Outlook Privilege Escalation Vulnerability”. Known Exploited Vulnerabilities Catalog, added 14 Mar 2023.
- ^ National Institute of Standards and Technology. “CVE-2023-23397 Detail”. National Vulnerability Database, published 14 Mar 2023.
- ^ Microsoft. Advisories and fixes: msrc.microsoft.com, msrc.microsoft.com, msrc.microsoft.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.972, percentile 99.9, 31 Oct 2026.
- CVE Program. “CVE-2023-23397”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.