CVE-2023-35311: Microsoft Outlook Security Feature Bypass Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 11 Jul 2023, the same day the CVE record was published.

How likely is exploitation in the next 30 days?

15.5%

EPSS score, percentile 96.8 of all scored records

How severe?

8.8 High

CVSS v3.1 base score, given by the CNA

What should I do?

Required action (CISA), due 1 Aug 2023: Apply updates per vendor instructions or discontinue use of the product if updates are unavailable.

Advisories and patches (1)

Which versions are affected?

Affected: 16.0.1; 16.0.1; 19.0.0; 16.0.0.0 up to, not including, 16.0.5404.1000; 14.0.0 up to, not including, 15.0.5571.1000; 15.0.0.0 up to, not including, 15.0.5571.1000

Versions by product

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

What to do

CISA due date for this action: 1 August 2023.

Advisories and patches

• Microsoft Outlook Security Feature Bypass Vulnerability (Vendor advisory)

Linked from CISA's catalog entry

• https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2023-35311
• https://nvd.nist.gov/vuln/detail/CVE-2023-35311

Affected products and versions

As listed in the CVE record.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

About this vulnerability

Microsoft Outlook contains a security feature bypass vulnerability that allows an attacker to bypass the Microsoft Outlook Security Notice prompt.

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2023-35311 to its Known Exploited Vulnerabilities (KEV) catalog on 11 Jul 2023.
• CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
• The due date CISA sets for the required action is 1 Aug 2023.
• The CVE record was published on 11 Jul 2023, the same day it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 8.8 (High), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 15.5% (percentile 96.8), as of 28 Oct 2026.
• CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact total.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.

Description

Microsoft Outlook Security Feature Bypass Vulnerability

Microsoft Outlook Security Feature Bypass Vulnerability

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Weakness

• CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

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