# CVE-1999-1463: Microsoft Windows NT IP stack improper fragment reassembly

Source: https://junglewise.ai/threats/cve-1999-1463-microsoft-windows-nt-ip-stack-improper-fragment-reassembly  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 1997-07-10. Updated: 2026-05-10  
License: CC BY 4.0 with a link back

CVE-1999-1463 · Severity: medium · CVSS 5 · Published 1997-07-10

A vulnerability in the networking component of Windows NT 4.0 allows remote attackers to disrupt system operations or bypass security filters. By sending specially crafted network traffic, an attacker can cause the system to crash or potentially sneak unauthorized data past a firewall. This could lead to unplanned downtime or a breach of network security policies.

Technologies: [Microsoft Windows Nt](https://junglewise.ai/threats/technologies/windows-nt). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-1999-1463 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-1999-1463 being exploited in the wild.

**How severe is CVE-1999-1463?** Medium severity, with a CVSS score of 5, published 10 July 1997.

**Which products and versions are affected?** Microsoft Windows NT 4.0 before Service Pack 3.

**Is there a fix for CVE-1999-1463?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-1999-1463 attacked?** It is attacked over the network, in an operating system.

**Am I affected by CVE-1999-1463?** Check whether you run Microsoft Windows Nt. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability exists in the TCP/IP stack of Windows NT 4.0 (prior to SP3) related to the handling of fragmented IP packets. The stack incorrectly reassembles sessions when receiving fragmented packets that lack the initial fragment, potentially treating them as a valid session. This flaw can be exploited by a remote, unauthenticated attacker to bypass firewall rules that rely on fragment inspection or to trigger a system crash (Denial of Service). The issue was addressed in Windows NT 4.0 Service Pack 3.

## Affected products

- Microsoft Windows NT 4.0 before Service Pack 3

## Timeline

- 1997-07-10: disclosed

## References

- [http://www.securityfocus.com/archive/1/7219](http://www.securityfocus.com/archive/1/7219)
- [https://exchange.xforce.ibmcloud.com/vulnerabilities/528](https://exchange.xforce.ibmcloud.com/vulnerabilities/528)

## Related threats

- [Microsoft Windows NT OS Kernel privilege escalation via integer underflow](https://junglewise.ai/threats/cve-2026-42980-microsoft-windows-nt-os-kernel-privilege-escalation-via-integer)
- [Microsoft Windows NT OS Kernel privilege escalation via integer underflow](https://junglewise.ai/threats/cve-2026-42916-microsoft-windows-nt-os-kernel-privilege-escalation-via-integer)
- [Microsoft Windows NT denial of service in SMB logon request](https://junglewise.ai/threats/cve-1999-0225-microsoft-windows-nt-denial-of-service-in-smb-logon-request)
- [Microsoft Windows TCP/IP stack denial of service in IP fragmentation](https://junglewise.ai/threats/cve-1999-0258-microsoft-windows-tcp-ip-stack-denial-of-service-in-ip)
- [War FTP buffer overflow allows remote command execution](https://junglewise.ai/threats/cve-1999-0256-war-ftp-buffer-overflow-allows-remote-command-execution)