Windows TCP/IP — CraftedSignal Threat Feed

CVE-2026-40415 Use-After-Free Vulnerability in Windows TCP/IP

hello@craftedsignal.io — Tue, 12 May 2026 18:49:27 +0000

CVE-2026-40415 is a critical use-after-free vulnerability residing within the Windows TCP/IP stack. Successful exploitation enables a remote, unauthorized attacker to execute arbitrary code within the context of the affected system. The vulnerability stems from improper memory management within the TCP/IP driver, which can be triggered by maliciously crafted network packets. Given its network-facing nature, this vulnerability poses a significant risk to Windows systems, potentially leading to complete system compromise and lateral movement within the network. This vulnerability was published May 12, 2026.

Attack Chain

Attacker identifies a vulnerable Windows system exposed on the network.
The attacker crafts a malicious TCP packet specifically designed to trigger the use-after-free condition in the Windows TCP/IP stack.
The attacker sends the malicious TCP packet to the target system.
The vulnerable TCP/IP driver processes the packet and attempts to access a memory region that has already been freed, leading to memory corruption.
The attacker leverages the memory corruption to overwrite critical system data or inject malicious code into memory.
The attacker gains control of the execution flow and executes arbitrary code within the context of the system.
The attacker establishes persistence on the compromised system (e.g., via registry modification or scheduled tasks).
The attacker performs lateral movement to other systems within the network or exfiltrates sensitive data.

Impact

Successful exploitation of CVE-2026-40415 allows a remote attacker to execute arbitrary code on a vulnerable Windows system. This can lead to complete system compromise, including data theft, system disruption, and further propagation of attacks within the network. Given the ubiquity of Windows systems, this vulnerability has the potential to affect a large number of organizations and individuals.

Recommendation

Apply the security update provided by Microsoft to patch CVE-2026-40415 immediately on all affected Windows systems.
Monitor network traffic for suspicious TCP packets that may indicate exploitation attempts, using the provided Sigma rule that detects anomalous TCP flags.
Enable Windows Firewall and restrict inbound TCP connections to only necessary ports to reduce the attack surface.
Implement network segmentation to limit the potential impact of a successful exploit.

CVE-2026-40414: Windows TCP/IP Null Pointer Dereference Denial-of-Service

hello@craftedsignal.io — Tue, 12 May 2026 18:49:12 +0000

CVE-2026-40414 describes a null pointer dereference vulnerability in the Windows TCP/IP stack. An attacker on an adjacent network can exploit this flaw to trigger a denial-of-service (DoS) condition. The vulnerability resides within the handling of specific TCP/IP packets, where a malformed or unexpected packet structure can lead to a null pointer dereference, crashing the system or rendering it unresponsive. This issue was reported to Microsoft and assigned a CVSS v3.1 score of 7.4. The vulnerability affects systems where the TCP/IP stack is exposed to adjacent networks, increasing the attack surface.

Attack Chain

Attacker identifies a target Windows system on an adjacent network.
Attacker crafts a malicious TCP/IP packet designed to trigger the null pointer dereference.
The attacker sends the crafted packet to the target system.
The Windows TCP/IP stack receives and processes the packet.
Due to the malformed structure of the packet, the TCP/IP stack attempts to dereference a null pointer.
This null pointer dereference causes the system to crash or become unresponsive.
The target system experiences a denial-of-service condition, impacting network connectivity and application availability.

Impact

Successful exploitation of CVE-2026-40414 results in a denial-of-service condition on the target Windows system. This can disrupt network communications, prevent access to critical services, and potentially lead to data loss or corruption if applications are abruptly terminated. The vulnerability is rated as HIGH severity with a CVSS base score of 7.4. The impact is limited to systems on adjacent networks, but could be significant for organizations relying on those systems for essential operations.

Recommendation

Apply the security update provided by Microsoft to patch CVE-2026-40414 as soon as possible, referenced in the Microsoft advisory.
Monitor network traffic for suspicious TCP/IP packets originating from adjacent networks using the Sigma rule.
Consider implementing network segmentation to limit the exposure of critical systems to adjacent networks.
Enable logging for network connections and analyze logs for unexpected patterns, as this could be indicative of exploitation attempts.

CVE-2026-40413: Windows TCP/IP Null Pointer Dereference Denial of Service

hello@craftedsignal.io — Tue, 12 May 2026 18:48:39 +0000

CVE-2026-40413 is a security vulnerability affecting Windows TCP/IP. The vulnerability, a null pointer dereference, allows an unauthorized attacker within an adjacent network to trigger a denial-of-service (DoS) condition. This vulnerability was published on May 12, 2026, and has a CVSS v3.1 score of 7.4. Exploitation of this vulnerability could disrupt network services and impact the availability of affected Windows systems. Defenders should apply the patch released by Microsoft to mitigate the risk.

Attack Chain

The attacker gains access to a network adjacent to the target Windows system.
The attacker sends a specially crafted TCP/IP packet to the target system.
The Windows TCP/IP stack attempts to process the malicious packet.
During packet processing, a null pointer is dereferenced due to the crafted packet’s structure.
The null pointer dereference causes the TCP/IP service to crash.
The crashed TCP/IP service leads to a denial-of-service condition, preventing legitimate network communication.
The target system becomes unresponsive to network requests.

Impact

Successful exploitation of CVE-2026-40413 leads to a denial-of-service condition on the targeted Windows system. This can disrupt network services, impacting availability and potentially causing data loss or corruption if critical processes are interrupted. The vulnerability can be exploited by an attacker on an adjacent network, increasing the risk in environments with shared network infrastructure.

Recommendation

Apply the security update provided by Microsoft to patch CVE-2026-40413 as referenced in the advisory URL.
Monitor network traffic for anomalous TCP/IP packets originating from adjacent networks using the Sigma rule “Detect CVE-2026-40413 Exploitation Attempt — Suspicious TCP Packet”.
Enable network intrusion detection systems to identify and block potentially malicious TCP/IP packets.

CVE-2026-40406 - Windows TCP/IP Use-After-Free Information Disclosure

hello@craftedsignal.io — Tue, 12 May 2026 18:47:43 +0000

CVE-2026-40406 is a use-after-free vulnerability affecting Windows TCP/IP. This flaw enables an unauthenticated attacker to potentially disclose sensitive information by exploiting memory management errors within the TCP/IP stack. Successful exploitation could lead to the exposure of kernel memory contents, potentially revealing cryptographic keys, user credentials, or other sensitive data. Given the widespread use of Windows operating systems, this vulnerability presents a significant risk to a broad range of users and organizations. Defenders should prioritize patching this vulnerability and implement appropriate network monitoring to detect and prevent exploitation attempts.

Attack Chain

The attacker sends a specially crafted network packet to the target system.
The packet triggers a use-after-free condition within the Windows TCP/IP stack.
The TCP/IP stack attempts to access a memory region that has already been freed.
Due to the use-after-free vulnerability, the memory now contains potentially sensitive data.
The TCP/IP stack incorporates this data into subsequent network communications.
The attacker intercepts the network communication.
The attacker extracts the leaked sensitive data from the intercepted communication.

Impact

Successful exploitation of CVE-2026-40406 could lead to the disclosure of sensitive information, such as cryptographic keys or user credentials, from the targeted Windows system. An attacker could use this information to further compromise the system or network. The impact is limited to information disclosure due to the nature of the use-after-free vulnerability in TCP/IP. The number of potential victims is extensive, encompassing any system running a vulnerable version of Windows.

Recommendation

Apply the security update provided by Microsoft to patch CVE-2026-40406, as referenced in the provided URL.
Implement network intrusion detection systems (IDS) to monitor for suspicious network traffic patterns that may indicate exploitation attempts targeting CVE-2026-40406.
Enable and review relevant Windows event logs related to network activity to identify potential anomalies or exploitation attempts.

CVE-2026-40401 - Windows TCP/IP Null Pointer Dereference Denial of Service

hello@craftedsignal.io — Tue, 12 May 2026 18:46:52 +0000

CVE-2026-40401 is a vulnerability affecting Windows TCP/IP, stemming from a null pointer dereference. This flaw allows an unauthorized, local attacker to trigger a denial-of-service (DoS) condition on the targeted system. The vulnerability was published by Microsoft and assigned a CVSS v3.1 base score of 7.1. An attacker leveraging this vulnerability could potentially disrupt network services and impact the availability of the system. The vulnerability requires local access and does not need user interaction to trigger the denial of service.

Attack Chain

The attacker gains local access to the targeted Windows system.
The attacker crafts a specific TCP/IP packet or network request.
The crafted packet triggers a null pointer dereference within the Windows TCP/IP stack.
The null pointer dereference causes the TCP/IP service to crash.
The crash disrupts network connectivity and related services.
The system experiences a denial-of-service condition, impacting availability.

Impact

Successful exploitation of CVE-2026-40401 can lead to a denial-of-service condition on the targeted Windows system. This disruption impacts network services, potentially affecting other applications and users relying on network connectivity. The impact is limited to local denial of service.

Recommendation

Apply the security update provided by Microsoft to patch CVE-2026-40401 as soon as possible (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40401).
Monitor systems for unexpected TCP/IP service crashes using the provided Sigma rules.

CVE-2026-34351: Windows TCP/IP Race Condition Privilege Escalation

hello@craftedsignal.io — Tue, 12 May 2026 18:25:19 +0000

CVE-2026-34351 is a security vulnerability affecting Windows TCP/IP. This vulnerability is a race condition, a type of flaw that occurs when multiple threads or processes access shared resources concurrently without proper synchronization. In this specific case, the lack of synchronization in Windows TCP/IP allows a local, authenticated attacker to exploit the vulnerability and escalate their privileges on the system. The vulnerability was published on May 12, 2026. Exploitation of this vulnerability could allow an attacker to gain higher-level access to the system, potentially leading to unauthorized data access, modification, or complete system compromise.

Attack Chain

Attacker obtains initial access to the system with valid user credentials.
Attacker identifies the vulnerable code path within the Windows TCP/IP stack related to shared resource access.
Attacker crafts a specific sequence of TCP/IP operations to trigger the race condition.
Attacker initiates multiple concurrent TCP/IP requests that attempt to access the shared resource simultaneously.
Due to the lack of proper synchronization, the race condition occurs, leading to an exploitable state within the TCP/IP stack.
Attacker leverages the exploitable state to overwrite critical system data or function pointers.
The overwritten data or function pointers are used by the system, causing it to execute attacker-controlled code.
Attacker gains elevated privileges on the system, completing the privilege escalation.

Impact

Successful exploitation of CVE-2026-34351 allows an attacker with local access to escalate their privileges on a vulnerable Windows system. This could lead to a complete compromise of the system, including unauthorized access to sensitive data, installation of malware, or disruption of services. The impact is significant because it allows a standard user to gain administrator-level control, bypassing security controls.

Recommendation

Apply the security update released by Microsoft to patch CVE-2026-34351 as detailed in the Microsoft Security Response Center advisory https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-34351.
Monitor for suspicious network activity and privilege escalation attempts after patching.
Deploy the Sigma rule “Detect Potential CVE-2026-34351 Exploitation - TCP/IP Concurrent Requests” to identify potential exploitation attempts by monitoring for unusual patterns of concurrent TCP/IP requests indicative of a race condition trigger.

CVE-2026-34334 Windows TCP/IP Race Condition Privilege Escalation

hello@craftedsignal.io — Tue, 12 May 2026 18:22:47 +0000

CVE-2026-34334 identifies a critical vulnerability in the Windows TCP/IP stack related to a race condition. This flaw allows an attacker with local access and authorization to elevate their privileges on the system. The vulnerability stems from improper synchronization when handling shared resources during concurrent execution within the TCP/IP protocol. Successful exploitation could grant the attacker higher-level permissions, potentially leading to complete system compromise. This issue was reported to Microsoft and assigned CVE-2026-34334 for tracking. Defenders should apply the patch released by Microsoft to mitigate the risk of exploitation.

Attack Chain

An attacker gains initial local access to a Windows system with a standard user account.
The attacker executes a specially crafted application designed to trigger the race condition within the Windows TCP/IP stack.
The application initiates multiple concurrent TCP/IP operations that access a shared resource.
Due to the improper synchronization, the concurrent operations collide, leading to an inconsistent state within the TCP/IP stack.
The attacker leverages this inconsistent state to overwrite critical system variables or function pointers related to privilege levels.
The attacker triggers a system call or function that relies on the manipulated privilege levels.
The system incorrectly grants elevated privileges to the attacker’s process due to the manipulated state.
The attacker performs privileged operations, gaining control over the system.

Impact

Successful exploitation of CVE-2026-34334 allows a locally authenticated attacker to elevate their privileges on a vulnerable Windows system. This can lead to the attacker gaining complete control over the affected machine, potentially resulting in data theft, malware installation, or denial of service. Given the widespread use of Windows, this vulnerability poses a significant risk to a large number of systems if left unpatched.

Recommendation

Apply the security update provided by Microsoft to patch CVE-2026-34334 on all affected Windows systems (Reference: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-34334).
Deploy the Sigma rules provided below to your SIEM to detect potential exploitation attempts targeting this vulnerability.
Monitor process creation events for suspicious executables or scripts being launched shortly after network activity, as this could indicate exploitation.