Is CVE-2026-55009 in the CISA KEV catalog?

No. CVE-2026-55009 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-55009?

CVE-2026-55009 has a CVSS v3 base score of 7.8 (HIGH).

How do I fix or mitigate CVE-2026-55009?

No published fix for CVE-2026-55009 has been found yet. Check the linked vendor advisories for guidance as it becomes available.

CVE & CISA-KEV Catalog

CVE-2026-55009

HIGH

7.8

CVSS v3

NVD

Description

Deserialization of untrusted data in Microsoft Exchange Server allows an authorized attacker to elevate privileges locally.

CWE-502Deserialization of Untrusted Data

How to fix

No published remediation has been found for this vulnerability's affected products yet.

Mitigation guidance may be in the linked vendor advisories in the References section below.

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CVSS v3 Vector

Exploitability

Attack VectorLocal

Attack ComplexityLow

Privileges RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Exploit Intelligence

EPSS data unavailable for this CVE.

References

Other references1

msrc.microsoft.com

Related Vulnerabilities

Other CWE-502 (Deserialization of Untrusted Data) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-0669	High	7.2	100%	KEV + Ransom	Fix
CVE-2021-44228	Critical	10.0	100%	KEV + Ransom	Fix
CVE-2021-35464	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2023-29300	Critical	9.8	100%	KEV + Ransom	-
CVE-2025-53770	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2022-41082	High	8.0	100%	KEV + Ransom	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-14.