CVE-2026-55006
Microsoft Exchange Server 2016 … 2019
Raw vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-55006 is a high-severity Insufficient Granularity of Access Control (CWE-1220) vulnerability in Microsoft Exchange Server. Its CVSS base score is 7.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Services File Permissions Weakness (T1574.010); ranked at the 22th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-24 (Access Control Decisions) and AC-3 (Access Enforcement) — see the control section below for these in your framework.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-44025
Vulnerability Data
Insufficient granularity of access control in Microsoft Exchange Server allows an authorized attacker to elevate privileges locally.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 3 hardening rules · 3 OS baselines
V16.4.2V8.4.2V11.7.1V13.2.4
Mitigating Controls (NIST 800-53 r5) AI
Least privilege explicitly demands that only the minimum necessary accesses are granted, eliminating the broad permissions that define this weakness.
AC-24 requires access decisions to be applied precisely and unambiguously to every request, structurally blocking insufficiently granular policies.
AC-3 requires enforcement of authorizations according to policy, directly compelling sufficiently granular rules so broad allowances cannot be introduced.
AC-4 enforces approved information flows with explicit source/destination rules, preventing overly coarse access policies from being deployed.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
PR.IR-01's segmentation + zero-trust rules directly enforce minimum-necessary access at network boundaries, removing most instances of overly broad policy; CWE-1220 can still exist in application-layer or intra-segment controls that this single outcome does not address.
PR.PS-06's general SDLC practices can surface granularity issues during design/review (partial prevention) but do not specifically target access-control policy breadth, so they remove only part of CWE-1220's risk.
CWE-1220 permits unauthorized access to sensitive assets but neither prevents nor impairs the delivery of adverse-event information to authorized recipients.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Directly requires information-access restriction at the level of individual assets and operations, addressing the granularity gap.
Establishes the overarching access-control policy whose granularity directly determines whether the weakness exists.
Defines the assignment and review of access rights; insufficient granularity in those rights is the root of CWE-1220.
Specifies management of privileged access rights, where overly broad privileges are a common manifestation of the weakness.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Windows Server 2016 (1 rule)
- V-225025 Local accounts with blank passwords must be restricted to prevent access from the network. prevents CWE-1220