CVE-2025-29971

What it actually does

CVE-2025-29971 is an out-of-bounds read vulnerability in Web Threat Defense's Windows kernel driver, WTD.sys. A remote, unauthenticated attacker can trigger the driver to read memory outside the intended buffer boundary, likely through crafted network traffic or input processed by the Web Threat Defense inspection path. The stated security impact is denial of service: malformed input can cause the driver or host operating system component to fault, crash, or become unstable rather than safely rejecting the input.

Why it matters to the business

Successful exploitation can interrupt systems running the affected Web Threat Defense driver, potentially causing endpoint or server crashes, service degradation, loss of network protection, and operational downtime. Because the attack is unauthenticated and network-reachable, exposed deployments should be treated as a priority even though public exploit maturity is currently listed as none and the vulnerability is not known to be in CISA KEV or ransomware campaigns. The EPSS score is elevated, indicating a meaningful probability of exploitation activity compared with typical vulnerabilities.

How an attack unfolds

An attacker first identifies systems or network paths where Web Threat Defense traffic inspection is active and reachable. They then send specially crafted network input that reaches the WTD.sys processing logic. Due to insufficient bounds checking, the driver reads beyond the expected memory region. In kernel-mode driver contexts, this can result in an access violation, bug check, driver crash, or broader system instability. The expected attacker objective is disruption rather than code execution: repeated triggering can create recurring denial of service until the vulnerable driver is updated, disabled, or shielded from malicious traffic.

How to fix it

Upgrade Web Threat Defense to a vendor-provided fixed release as soon as available and ensure the WTD.sys driver is replaced by the patched version. No exact fixed versions were provided in the input, so administrators should consult the vendor advisory for CVE-2025-29971 and deploy the recommended update across all affected systems. If immediate patching is not possible, reduce exposure by restricting untrusted network traffic to systems using Web Threat Defense, disabling vulnerable inspection features where vendor-supported, isolating high-risk systems, and monitoring for crashes or repeated driver faults. Avoid relying solely on perimeter filtering because the vulnerable component may process traffic before higher-level controls can reject it.

How to confirm the fix worked

Confirm whether WTD.sys is present and determine its file version, build timestamp, and digital signature status on systems running Web Threat Defense. Compare installed product and driver versions against the vendor advisory for CVE-2025-29971 and verify that the patched driver is loaded after reboot. Validate that systems no longer produce WTD.sys-related bug checks, service crashes, or Windows Error Reporting events under normal traffic. Where authorized, perform controlled vendor-approved regression or vulnerability validation testing in a non-production environment to confirm that malformed network input no longer causes instability.

Typical attack path

1. Identify hosts, gateways, or endpoints running the vulnerable Web Threat Defense driver WTD.sys.
2. Determine whether the vulnerable network inspection path can be reached remotely.
3. Send crafted network traffic or protocol input designed to trigger the out-of-bounds read condition.
4. Cause WTD.sys or the host system to fault, crash, or become unstable.
5. Repeat exploitation to sustain denial of service or to disrupt security monitoring and network protection.

How to detect it

Look for evidence of attempted or successful denial of service rather than post-exploitation persistence. Relevant sources include Windows System logs, Windows Error Reporting logs, application/service logs from Web Threat Defense, endpoint detection telemetry, crash dump directories, and network telemetry showing unusual malformed or high-volume traffic immediately before crashes. Search for bug checks, driver faults, service terminations, unexpected reboots, and dump files referencing WTD.sys. Correlate repeated WTD.sys failures across multiple hosts or at similar times with inbound network activity from common external sources. Because no public exploit maturity or named threat actor activity is provided, detection should focus on crash artifacts and anomalous traffic patterns rather than actor-specific tooling.

• WTD.sys
• Event ID 1001
• BugCheck
• Windows Error Reporting
• faulting module WTD.sys
• DRIVER_IRQL_NOT_LESS_OR_EQUAL
• PAGE_FAULT_IN_NONPAGED_AREA
• SYSTEM_SERVICE_EXCEPTION
• C:\Windows\System32\drivers\WTD.sys
• C:\Windows\Minidump\
• C:\ProgramData\Microsoft\Windows\WER\ReportArchive\
• C:\ProgramData\Microsoft\Windows\WER\ReportQueue\

What your security team should do

• Inventory systems running Web Threat Defense and specifically identify hosts with WTD.sys installed or loaded.
• Prioritize patching of internet-facing, DMZ, remote-access, and high-availability systems because exploitation is unauthenticated and network-based.
• Monitor for WTD.sys crashes, Windows bug checks, unexpected reboots, and service restarts that could indicate attempted denial-of-service exploitation.
• Review vendor advisories for exact affected and fixed versions, then standardize all deployments on the fixed release.
• Temporarily restrict untrusted traffic paths to vulnerable systems if patching cannot be completed quickly.
• Create SIEM detections for WTD.sys fault events, bug checks, and Windows Error Reporting records involving the driver.
• After remediation, verify driver replacement and reboot status so the vulnerable kernel driver is not still loaded in memory.