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CVE-2026-55007 – Remote Code Execution (Double Free) – Microsoft Exchange Server 2019 (CU14/CU15) an

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Summary

CVE-2026-55007 is a double free (CWE-415) memory corruption vulnerability in Microsoft Exchange Server that allows an unauthorized attacker to execute code over a network. The flaw affects on-premises Exchange Server 2019 (Cumulative Update 14 and 15) and Exchange Server Subscription Edition RTM. Microsoft rates the vulnerability High severity with a CVSS v3.1 base score of 8.1.

Technical details

  • Root cause: a double free condition (CWE-415) in Exchange Server’s memory management, where a memory region is freed more than once, corrupting the heap.
  • Attack vector: exploitable over the network (AV:N) with no privileges required (PR:N) and no user interaction (UI:N).
  • Trigger conditions: high attack complexity (AC:H), meaning exploitation requires conditions outside the attacker’s direct control or additional preparatory steps.
  • Impact: successful exploitation allows an attacker to execute arbitrary code on the Exchange server, with the vulnerability rated as having high impact to confidentiality, integrity, and availability (C:H/I:H/A:H) under an unchanged scope (S:U).

Affected software

  • Microsoft Exchange Server 2019 Cumulative Update 14 — versions 15.02.0.0 up to (not including) 15.02.1544.046
  • Microsoft Exchange Server 2019 Cumulative Update 15 — versions 15.02.0.0 up to (not including) 15.02.1748.051
  • Microsoft Exchange Server Subscription Edition RTM — versions 15.02.0.0 up to (not including) 15.02.2562.049
  • All listed versions apply to x64-based systems.

Severity

  • CVSS v3.1 Base Score: 8.1 (High)
  • Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: apply the Microsoft security update that brings Exchange Server 2019 CU14 to 15.02.1544.046 or later, CU15 to 15.02.1748.051 or later, and Exchange Server Subscription Edition to 15.02.2562.049 or later.
  • If patching cannot be applied immediately: restrict and monitor network access to Exchange Server management and messaging endpoints, ensure Exchange servers are not unnecessarily exposed to the internet, and follow Microsoft’s standard Exchange Server hardening guidance until the update can be deployed.
  • Verify patch level using the Exchange Server Health Checker or by checking the build number against the fixed versions above.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Named response header x-owa-version (value itself)
  • Page title: Outlook Web Access, Outlook Web App
  • Raw response body: /owa/auth/<version>/, /ecp/<version>/, /owa/?Application=Exchange, OwaPage = ASP.auth_logon.aspx, owaauth.dll

References

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How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
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