CVE-2023-21556

CVE-2023-21556 is a high-severity vulnerability in Microsoft Windows 10 1607 with a CVSS 3.x base score of 8.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-191.

Key facts

• Severity: High (CVSS 3.x base score 8.1)
• EPSS exploit prediction: 1% (70th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-191
• Affected product: Microsoft Windows 10 1607
• Published: 2023-01-10
• Last modified: 2026-06-17

Description

Windows Layer 2 Tunneling Protocol (L2TP) Remote Code Execution Vulnerability

Frequently asked questions

What is CVE-2023-21556?

Windows Layer 2 Tunneling Protocol (L2TP) Remote Code Execution Vulnerability

How severe is CVE-2023-21556?

CVE-2023-21556 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2023-21556 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-21556?

CVE-2023-21556 primarily affects Microsoft Windows 10 1607. In total, 31 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2023-21556?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2023-21556 published?

CVE-2023-21556 was published on 2023-01-10 and last updated on 2026-06-17.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21556

Affected products (31)

• cpe:2.3:o:microsoft:windows_10_1607:-:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_10_1607:-:*:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_10_1809:-:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_10_1809:-:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_10_1809:-:*:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_10_20h2:-:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_10_20h2:-:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_10_20h2:-:*:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_10_21h2:-:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_10_21h2:-:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_10_21h2:-:*:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_10_22h2:-:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_10_22h2:-:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_10_22h2:-:*:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_11_21h2:-:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_11_21h2:-:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_11_22h2:-:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_11_22h2:-:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_7:-:sp1:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_7:-:sp1:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_8.1:-:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_8.1:-:*:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_rt_8.1:-:*:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2008:-:sp2:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_server_2008:-:sp2:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_server_2008:r2:sp1:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_server_2012:-:*:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2012:r2:*:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2016:-:*:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2019:-:*:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2022:-:*:*:*:*:*:*:*

More vulnerabilities in Microsoft Windows 10 1607

• CVE-2026-47291 — Critical (CVSS 9.8): Integer overflow or wraparound in Windows HTTP.sys allows an unauthorized attacker to execute code over a network.
• CVE-2026-44815 — Critical (CVSS 9.8): Stack-based buffer overflow in Windows DHCP Client allows an unauthorized attacker to execute code over a network.
• CVE-2026-33824 — Critical (CVSS 9.8): Double free in Windows IKE Extension allows an unauthorized attacker to execute code over a network.
• CVE-2025-60724 — Critical (CVSS 9.8): Heap-based buffer overflow in Microsoft Graphics Component allows an unauthorized attacker to execute code over a…
• CVE-2025-53766 — Critical (CVSS 9.8): Heap-based buffer overflow in Windows GDI+ allows an unauthorized attacker to execute code over a network.
• CVE-2025-47981 — Critical (CVSS 9.8): Heap-based buffer overflow in Windows SPNEGO Extended Negotiation allows an unauthorized attacker to execute code over…

All CVEs affecting Microsoft Windows 10 1607 →

Other CWE-191 (Integer Underflow) vulnerabilities

• CVE-2007-0063 — Critical (CVSS 10.0): Integer underflow in the DHCP server in EMC VMware Workstation before 5.5.5 Build 56455 and 6.x before 6.0.1 Build…
• CVE-2026-53176 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: IB/isert: Reject login PDUs shorter than…
• CVE-2026-37534 — Critical (CVSS 9.8): Integer underflow vulnerability in Open-SAE-J1939 thru commit b6caf884df46435e539b1ecbf92b6c29b345bdfe (2025-11-30) in…
• CVE-2025-52471 — Critical (CVSS 9.8): ESF-IDF is the Espressif Internet of Things (IOT) Development Framework. An integer underflow vulnerability has been…
• CVE-2025-29909 — Critical (CVSS 9.8): CryptoLib provides a software-only solution using the CCSDS Space Data Link Security Protocol - Extended Procedures…
• CVE-2024-47606 — Critical (CVSS 9.8): GStreamer is a library for constructing graphs of media-handling components. An integer underflow has been detected in…

Browse all CWE-191 (Integer Underflow) vulnerabilities →