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CVE-2026-54997 is a medium-severity information disclosure vulnerability in the Windows Server Message Block (SMB) protocol implementation. The flaw stems from the SMB server component’s failure to properly initialize certain memory resources before utilizing them in processing client requests. This uninitialized resource access falls under CWE-908 (Use of Uninitialized Resource) and CWE-457 (Improper Initialization).
The vulnerability requires an attacker to have already established authorized local access to the target system—either through a low-privilege account, a compromised user session, or code execution context. It cannot be exploited remotely over the network; anonymous attackers cannot simply send crafted traffic to TCP port 445 to trigger the flaw. Instead, the attack becomes relevant after an attacker has gained a foothold via another vector, such as a malicious program, vulnerable service, or compromised credential.
When the SMB server processes certain file-sharing or authentication requests, it attempts to read from memory locations that have not been initialized with valid data structures. This can expose sensitive residual data from adjacent memory regions, including cached credentials, session tokens, NTLM hashes, memory addresses, or other confidential process data. The exact SMB operation that triggers the flaw has not been publicly disclosed by Microsoft.
The attack complexity is low, requires no user interaction, and confidentiality impact is rated high—but integrity and availability are unaffected. The vulnerability does not by itself allow code execution, privilege escalation, or system crashes. However, disclosed information can be leveraged for credential theft, lateral movement, or bypassing exploit mitigations in combination with other vulnerabilities. Enterprise environments that rely heavily on SMB for file sharing and network resource access are particularly at risk.
Microsoft shipped fixes in the July 14, 2026 security updates across all supported Windows versions. The flaw was not publicly disclosed or known to be exploited prior to the update release.
DailyCVE Form:
Platform: Windows SMB
Version: 10/11/Server (multiple)
Vulnerability: Uninitialized resource disclosure
Severity: 5.5 MEDIUM
date: 2026-07-14
Prediction: Patched (July 2026)
What Undercode Say:
Analytics
- CVSS 3.1 Vector: `AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N`
– EPSS Score: < 1% (low likelihood of exploitation) - CISA KEV: Not catalogued
- SSVC: Automatable: No | Exploitation: None | Technical Impact: Partial
- Affected Products: Windows 10 (1607, 1809, 21H2, 22H2), Windows 11 (24H2, 25H2, 26H1), Windows Server (2012–2025)
- Fixed Build Thresholds: Windows 11 24H2/25H2 → 26100.8875; Windows 10 22H2 → 19045.7548
Bash / PowerShell Commands
Check current Windows build number
Alternative: Get full build info
Get-ComputerInfo | Select-Object WindowsVersion, WindowsBuildLabEx
Check SMB service status
Get-Service -Name LanmanServer | Select-Object Status, DisplayName
Verify SMB protocol versions enabled
Get-SmbServerConfiguration | Select-Object EnableSMB1Protocol, EnableSMB2Protocol
Check installed updates for July 2026 (look for KB matching the month)
Get-HotFix | Where-Object { $<em>.InstalledOn -gt (Get-Date).AddDays(-30) } |
Select-Object HotFixID, Description, InstalledOn
Check if SMB-related patches are installed (example filter)
Get-HotFix | Where-Object { $</em>.HotFixID -like "202607" }
Restart SMB service after patching (requires admin)
Restart-Service -Name LanmanServer -Force
Exploit:
Exploitation requires local, authenticated access. An attacker with a low-privilege account on the target system can invoke specific SMB operations that trigger the uninitialized memory read. Because the flaw lies in the SMB server component, the attacker does not need to send network packets to port 445—they can interact with the local SMB stack through authenticated local API calls or by mounting/accessing SMB shares from the same machine. The uninitialized memory may contain cached credentials, session keys, or other sensitive data from privileged processes. Successful exploitation discloses that information to the attacker’s process, enabling credential reuse, privilege escalation chaining, or further system reconnaissance. No user interaction is required.
Protection:
- Apply the July 2026 cumulative security update immediately from Windows Update or Microsoft Update Catalog.
- Restart the SMB service or reboot after patching to ensure the fix is fully activated.
- Restrict local SMB access to only essential users and remove unnecessary local accounts.
- Enable strict access controls on SMB services and monitor for unusual access patterns.
- Disable unnecessary SMB features (e.g., SMBv1 if not required).
- Implement network segmentation to limit the blast radius of local information disclosure.
- Maintain proper logging to detect suspicious access or memory disclosure attempts.
Impact:
- Confidentiality: High – Sensitive memory contents (credentials, tokens, cached data) can be exposed to an unauthorized local process.
- Integrity: None – The vulnerability does not allow data modification.
- Availability: None – No system crashes or denial of service.
- Privilege Escalation: Indirect – Disclosed information can be chained with other vulnerabilities to elevate privileges or move laterally.
- Enterprise Risk: Significant in environments using SMB for file sharing; insider threats or attackers with initial access can harvest sensitive data.
- Lateral Movement: Credential leakage can facilitate further network compromise.
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Sources:
Reported By: nvd.nist.gov
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