CVE-2026-21509
Microsoft Office: Security Feature Bypass
As of , CVE-2026-21509 in Microsoft Office is on CISA's list of exploited vulnerabilities: CISA listed it on . Our patch-first group: Patch this week.
- Exploited
- Yes: CISA listed it on 26 January 2026
- US federal deadline
- 16 February 202621 days after CISA listed it. US federal civilian agencies must fix it by then.
- Used in ransomware campaigns
- Not known to CISA
- EPSS score
- 0.71Higher than 99% of the CVEs EPSS scores. EPSS estimates the chance of exploitation activity in the next 30 days.
- Public exploit
- None foundNeither Metasploit nor Exploit-DB lists one.
- Fix
- Vendor advice: msrc.microsoft.comLinks below, from CISA's entry.
What CISA says to do
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
CISA's required action
- msrc.microsoft.comPlease adhere to Microsoft’s recommended guidelines to address this vulnerability. Implement all final mitigations provided by the vendor…
What the flaw is
Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.
CISA's description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
The CVE record's description, from microsoft
- CVE published
- 26 January 2026
- Assigned by
- microsoft
- CVSS
- 7.8 High (CVSS 3.1, from the CNA)
- CWE-807
- Reliance on Untrusted Inputs in a Security Decision
- CISA SSVC, exploitation
- active
- CISA SSVC, automatable
- no
- CISA SSVC, technical impact
- total
Timeline
- The CVE record was published.
- CISA added it to its list of exploited vulnerabilities.
- CISA changed its entry. Edited: description.
- The US federal deadline to fix it.
Office: other exploited entries
| Vulnerability | Product | Our group | Listed | Deadline | EPSS |
|---|---|---|---|---|---|
| CVE-2010-3333Stack-based Buffer Overflow | Microsoft Office | Patch this weekMetasploit module; EPSS 0.89; verified Exploit-DB entry | 0.89 | ||
| CVE-2016-3235OLE DLL Side Loading | Microsoft Office | Patch this weekMetasploit module; verified Exploit-DB entry | 0.43 | ||
| CVE-2017-11882Memory Corruption | Microsoft Office | Patch this weekRansomware use; Metasploit module; EPSS 0.99 | 0.99 | ||
| CVE-2009-0556PowerPoint Code Injection | Microsoft Office | Patch this weekEPSS 0.67 | 0.67 | ||
| CVE-2023-23397Outlook Privilege Escalation | Microsoft Office | Patch this weekEPSS 0.97 | 0.97 | ||
| CVE-2009-0563Buffer Overflow | Microsoft Office | Patch this weekEPSS 0.63 | 0.63 | ||
| CVE-2013-1331Buffer Overflow | Microsoft Office | Patch this weekEPSS 0.80 | 0.80 | ||
| CVE-2012-1856MSCOMCTL.OCX Remote Code Execution | Microsoft Office | Patch this weekEPSS 0.72 | 0.72 | ||
| CVE-2015-2545Malformed EPS File | Microsoft Office | Patch this weekEPSS 0.86 | 0.86 | ||
| CVE-2016-7193Memory Corruption | Microsoft Office | Patch this weekEPSS 0.58 | 0.58 |
Read further
- CVE recordcve.org
- NVD entrynvd.nist.gov
- CISA's catalogcisa.gov
- EPSS for this CVEapi.first.org