[Update] Vulnerability in Microsoft Outlook (February 15, 2024)
Actively exploited. At least one CVE in this advisory is listed in the CISA Known Exploited Vulnerabilities catalog — exploitation has been observed in the wild. Treat remediation as urgent.
[Update on March 15, 2024] Added clarification regarding NTLM challenge-responses [Update on February 22, 2024] Added recommendations and clarifications on the functioning of the vulnerability. The vulnerability CVE-2024-21413 allows an attacker to bypass security measures...
CSIRTS triage
- What
- A vulnerability allows an attacker to bypass security measures.
- Who is affected
- Users of Microsoft Outlook are affected.
- Urgency
- Remediation is urgent as the vulnerability has been exploited in the wild.
- Action
- Follow the recommendations and apply the necessary updates.
AI-assisted analysis generated from the source advisory — verify against the original.
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Details
Original advisory: https://www.cert.ssi.gouv.fr/alerte/CERTFR-2024-ALE-005/
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Exploitation confirmedCVE-2024-21413Already exploited in the wild (CISA KEV) — the prediction phase is over. Patch now. Riskier than 100% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2024-21413 | coverage & exploitation status | NVD · CVE.org |
Same CVEs, other sources
How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.
- criticalexploitedCVE-2024-21413: Microsoft Outlook Improper Input Validation Vulnerabilitycisa-kev
Recent advisories for Microsoft Outlook
A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.
- mediumCVE-2025-59868: HCL Traveler for Microsoft Outlook (HTMO) is susceptible to a sensitive data exposure vulnerab…nvd · 2026-06-27
- highCVE-2023-37524: HCL Traveler for Microsoft Outlook (HTMO) is susceptible to vulnerabilities due to .NET Framew…nvd · 2026-06-27
- mediumCVE-2024-23581: The HCL Traveler for Microsoft Outlook libraries are being flagged as potentially malicious so…nvd · 2026-06-26
- highCVE-2026-45456: Microsoft Outlook and Word Remote Code Execution Vulnerabilitymsrc · 2026-06-09
- highCVE-2026-45458: Microsoft Outlook and Word Remote Code Execution Vulnerabilitymsrc · 2026-06-09
- highCVE-2026-47635: Microsoft Outlook and Word Remote Code Execution Vulnerabilitymsrc · 2026-06-09
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