CVE-2014-6321: Microsoft Schannel remote code execution via crafted packets

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 18 September 2026. Confidence: high.

critical priorityCVSS 2.0 base score of 10 with network reachability, no authentication, and complete impact, plus very high EPSS, makes this a top remediation priority.

What it is

Schannel, the Windows TLS/SSL implementation, mishandles crafted packets, allowing remote code execution. The flaw affects a broad set of Windows client and server releases, including Server 2003 through Server 2012 R2. Because Schannel is used by many services, exposure is wide and the flaw is remotely reachable without credentials.

Impact

A remote attacker can execute arbitrary code in the context of the affected service, potentially leading to full system compromise. Given the network vector and complete confidentiality, integrity and availability impact, the worst case is total host takeover.

Attack surface

Reached over the network by sending crafted packets to a service that uses Schannel for TLS/SSL. No authentication or user interaction is required per the AV:N/AC:L/Au:N vector.

Exploitation

Public exploit write-ups are referenced, and EPSS is very high (0.95988, 99.872nd percentile), indicating elevated likelihood of exploitation. The CVE is not listed in CISA KEV, so confirmed in-the-wild use is not established by this record.

What to do

• Apply the Microsoft MS14-066 security update to all affected Windows versions as the primary fix.
• Where patching cannot be immediate, restrict network access to TLS/SSL services using Schannel to trusted sources.
• Disable or remove unnecessary TLS/SSL listeners and services that rely on Schannel.
• Monitor vendor advisories and re-scan for unpatched legacy systems such as Server 2003 and Vista.
• Consider network segmentation to limit reachability of exposed Schannel endpoints.

Detection

• Monitor for crashes or unexpected restarts of services that use Schannel (IIS, RDP, LDAP over SSL).
• Inspect network traffic for malformed or anomalous TLS handshake packets targeting Schannel endpoints.
• Correlate host logs for suspicious child processes spawned by TLS-terminating services.
• Track patch status of affected Windows versions and alert on systems still missing MS14-066.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.