Security readout for executives and security teams
Plain-English summary
This high-severity AD FS flaw can let an already authorized, low-privilege local attacker gain greater control of an affected Windows system. Successful exploitation could compromise data confidentiality, integrity, and availability. Because CISA lists it as known exploited, organizations running AD FS should treat remediation as urgent.
Executive priority
Urgent. AD FS supports identity and authentication, and successful privilege escalation could enable broad system compromise. CISA's known-exploited designation materially raises near-term risk. Direct teams to identify affected AD FS hosts, apply Microsoft updates promptly, and investigate suspicious privilege activity rather than waiting for routine patch cycles.
Technical view
CVE-2026-56155 is an access-control granularity weakness in Active Directory Federation Services, classified as CWE-1220. It requires local access and low privileges, but no user interaction; attack complexity is low. CVSS 3.1 rates it 7.8, with potentially high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is most likely where AD FS operates on the listed Windows Server releases, including relevant Server Core installations. Windows 10 versions also appear in the affected-product data. The bundle does not identify vulnerable roles, configurations, update levels, or exact fixed builds, so asset-level verification against Microsoft guidance is required.
Exploitation context
CISA KEV status supports active exploitation in the wild. The supplied sources do not describe campaigns, affected organizations, exploitation volume, indicators, or technical methods. Exploitation still requires an authorized attacker with local, low-privilege access, making compromised accounts and existing system access important risk factors.
Researcher notes
The available evidence establishes local, authenticated, low-complexity privilege escalation and high potential impact. It does not provide root-cause detail beyond insufficient access-control granularity, affected AD FS configurations, fixed build numbers, indicators, or exploitation telemetry. Avoid inferring remote exploitability or specific post-exploitation capabilities from the supplied record.
Mitigation direction
- Apply the applicable Microsoft security update identified in the MSRC advisory.
- Prioritize internet-facing or identity-critical AD FS servers and systems with untrusted local users.
- Restrict local access and administrative pathways until affected systems are updated.
- Review Microsoft and CISA guidance for any additional mitigations or required deadlines.
Validation and detection
- Inventory AD FS deployments and map their operating-system versions against the affected list.
- Verify installed updates against the fixed versions or packages specified by Microsoft.
- Confirm low-privilege users cannot obtain unnecessary local access to AD FS hosts.
- Review identity-server logs for unexpected privilege changes or unusual local account activity.
- Re-scan remediated systems and document exceptions requiring compensating controls.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-1220: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupPrivilege behavior lookup
The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-56155 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.8 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C1.85.9microsoftVulnerability scoring details
Base CVSS 3.1 score
7.8HighVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- Added to KEVCISA-ADP
CISA Known Exploited Vulnerabilities metadata lists this CVE as known exploited.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- Active Directory Federation Services Elevation of Privilege VulnerabilityCVE reference, microsoft · vendor-advisory, patch
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-56155CVE reference, CISA-ADP · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Insufficient Granularity of Access Control
Insufficient Granularity of Access Control represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.