Vulnerability report

Trusted Third Party Report Confirmed Confidence In CISA KEV

CVE-2023-35311

Microsoft Outlook Security Feature Bypass Vulnerability

Microsoft 365 Apps for Enterprise · affected before https://aka.ms/OfficeSecurityReleases

Watch CVE-2023-35311 Browse KEV feed
Severity
CVSS 8.8 · High
Confidence
Confirmed
Exploit status
Trusted Third Party Report
EPSS
15.5%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2023-35311 is an unauthenticated Microsoft Outlook Security Feature Bypass Vulnerability.

Have exploitation attempts been observed?

Yes. Exploitation attempts have been reported for this vulnerability. Previdian lists it as a known exploited vulnerability. Listed in CISA KEV. Confidence is confirmed.

Who is affected?

Affected products include Microsoft 365 Apps for Enterprise and 5 other products, including affected before https://aka.ms/OfficeSecurityReleases, affected before https://aka.ms/OfficeSecurityReleases, and affected before 16.0.5404.1000.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

Microsoft Outlook Security Feature Bypass Vulnerability

Microsoft Outlook Security Feature Bypass Vulnerability

Microsoft Affected
Microsoft 365 Apps for Enterprise
Before https://aka.ms/OfficeSecurityReleases
Microsoft Affected
Microsoft Office LTSC 2021
Before https://aka.ms/OfficeSecurityReleases
Microsoft Affected
Microsoft Office 2019
Before https://aka.ms/OfficeSecurityReleases
Microsoft Affected
Microsoft Outlook 2016
Before 16.0.5404.1000
Microsoft Affected
Microsoft Outlook 2013
Before 15.0.5571.1000
Microsoft Affected
Microsoft Outlook 2013 Service Pack 1
Before 15.0.5571.1000
View vendor advisory (opens in new tab)
Published
11 Jul 2023
Exploitation Attempts Reported
11 Jul 2023
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
Required

Tags

microsoft cisa nessus_scanner

CVE References

Exploitation evidence

Evidence of exploitation attempts

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploitation Attempts Observed in the Wild

CISA

Recorded 11 Jul 2023

A trusted third party reported exploitation attempts.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
CISA First 2023-07-11 00:00 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nessus https://www.tenable.com/plugins/nessus/178203 02 Jun 2025

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

8.8 High

Potential damage if exploited. Separate from whether attackers are using it.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

EPSS

15.5%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

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

Timeline

From disclosure to observed exploitation attempts

  1. 09:26 UTC

    Nessus plugin available

    Scanner coverage available

  2. 17:03 UTC

    CVE published

    Vulnerability disclosed publicly

  3. 00:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  4. 23:09 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

Start 14-day Pro trial Read API docs
  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2023-35311

Sample API response 
{
  "cve_id": "CVE-2023-35311",
  "confidence": "Confirmed",
  "cvss_score": 8.8,
  "cvss_estimated": false,
  "epss_score": 0.15522,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}