BigDiskBuster Can Freeze Microsoft Defender Updates Without Shutting Down Antivirus Protection

Defender can keep running while its protection data goes stale

Security researcher Abdelhamid Naceri, better known as Chaotic Eclipse, has released BigDiskBuster, a proof-of-concept tool targeting the Microsoft Defender update mechanism.

The claimed zero-day does not immediately disable Defender or remove its existing protection. Instead, it prevents the antivirus product from receiving platform and signature updates while the tool remains active.

That distinction defines the risk. An affected endpoint may continue displaying Defender as operational while relying on increasingly outdated detection content and platform components. Newer malware could consequently evade protections that depend on subsequent signatures or product updates.

As of September 22, 2026, BigDiskBuster has no reported CVE identifier, Microsoft advisory, CVSS score, or vendor-confirmed remediation. The precise date on which the PoC was first released has not been disclosed in the available reporting.

Microsoft had not immediately commented when BleepingComputer reported the disclosure. There is also no evidence that attackers are exploiting the issue in the wild.

The claimed scope covers supported Windows versions, but exact builds remain unknown

Naceri says BigDiskBuster works across all supported Windows versions. However, no affected editions, operating-system build numbers, Defender platform releases, or signature versions have been identified.

The claim therefore remains broad and incompletely validated. Organizations cannot currently determine exposure by comparing their installed software against a documented range of vulnerable and fixed versions.

The directly affected component is Microsoft Defender, also called Windows Defender in the reporting. The flaw concerns its ability to obtain two categories of security content:

• Defender platform updates
• Malware signature or definition updates

BigDiskBuster reportedly needs to continue running in the background to maintain the block. Stopping the process may therefore end its immediate effect, although no independent technical analysis or official recovery procedure has been published.

The required privilege level is also unknown. Reporting describes BigDiskBuster as similar to UnDefend, a separate Defender issue released in April 2026 that allowed standard users to block definition updates. That privilege characteristic has not been established for BigDiskBuster and should not be assumed.

No remote attack path has been reported. The descriptions point to local execution of the PoC, but there is no formal attack-vector assessment or complete technical write-up establishing the access conditions.

The attack targets update availability rather than code execution

BigDiskBuster is best classified as a denial-of-service condition affecting endpoint protection updates. Its immediate security impact is availability, not direct system compromise.

There is no report that the technique independently enables:

• Arbitrary code execution
• Privilege escalation
• Credential or data theft
• Modification of user files
• Persistent access after the tool stops
• Complete termination of Microsoft Defender

The practical danger develops over time. If an attacker can keep BigDiskBuster running, the endpoint may remain fixed at its currently installed platform and signature versions.

Defender could still detect threats covered by that existing content. It may, however, miss malware addressed by later signatures or lose improvements delivered through subsequent platform updates.

This creates an ambiguous operational state: antivirus protection remains present, but its update pipeline is unavailable. Administrators who monitor only whether the Defender service is running could overlook the degradation.

The current PoC appears to have significant limitations. SecurityAffairs describes BigDiskBuster as buggy and requiring further rewriting, while Naceri has similarly characterized it as incomplete.

That may reduce the reliability of immediate attacks, but it is not a durable defense. Public PoCs can be studied, repaired, or reimplemented by other researchers and threat actors.

No CVE, KEV deadline, or confirmed exploitation

BigDiskBuster has not been assigned a reported CVE identifier. No CISA Known Exploited Vulnerabilities catalog entry, addition date, or federal remediation deadline has been identified.

There is likewise no reported evidence of active exploitation. The available information therefore supports treating BigDiskBuster as a publicly disclosed, claimed zero-day with an unstable PoC—not as a confirmed in-the-wild campaign.

Its severity remains difficult to quantify without several missing details. Researchers have not established the required permissions, the precise vulnerable code path, the range of affected builds, or whether ordinary security controls can reliably prevent execution.

Risk will vary by environment. Systems that use Microsoft Defender as their primary protection layer and lack independent telemetry face greater consequences from an extended update interruption.

The impact could be lower where application control prevents unauthorized tools from running, or where separate EDR and network-monitoring systems can expose suspicious activity. Those controls do not fix the underlying issue, but they can reduce reliance on Defender signatures alone.

The release follows a series of Windows security disclosures

BigDiskBuster is one of numerous exploit releases associated with Naceri, who also uses the names Nightmare Eclipse, INFINITE NIGHTMARE, and MSNightmare.

Since April 2026, he has reportedly published almost a dozen zero-day exploits amid a dispute with Microsoft over what he describes as an unfair termination in March 2025. He claims to be a former Microsoft employee.

His Defender-related releases include UnDefend, ShieldCrash, ShieldBreak, RoguePlanet, RedSun, YellowKey, GreenPlasma, and MiniPlasma. Other disclosures have targeted BitLocker and additional Windows components.

Microsoft reportedly fixed ShieldBreak, RoguePlanet, YellowKey, GreenPlasma, and MiniPlasma. Other publicly released issues were still described as lacking official patches, although the current status of every individual disclosure is not known.

ShieldCrash is claimed to provide SYSTEM access, while ShieldBreak was a Defender privilege-escalation issue. Those alleged capabilities must not be attributed to BigDiskBuster, which has only been reported to interfere with updates.

Naceri has also released claimed exploits against products from Nvidia, Kaspersky, Gen Digital, and CrowdStrike. Those disclosures provide context for his recent activity but do not indicate that BigDiskBuster affects those vendors.

Defenders should watch update health and background execution

There is currently no confirmed Microsoft patch, supported workaround, or Defender version known to be immune. Administrators should avoid making unverified system changes based solely on the public PoC.

The most useful immediate step is to monitor Defender update health rather than checking only whether antivirus services are enabled. Repeated failures involving both platform and signature updates deserve investigation.

Security teams should also:

1. Alert on endpoints whose Defender content stops advancing unexpectedly.
2. Correlate update failures with newly launched or continuously running background processes.
3. Search software inventories and endpoint telemetry for unauthorized copies of BigDiskBuster, UnDefend, or related PoCs.
4. Review process-creation and persistence events around the start of an update interruption.
5. Use application control to restrict unapproved executables where operationally feasible.
6. Retain independent EDR, network, and behavioral telemetry rather than relying solely on Defender signatures.
7. Track Microsoft security guidance for a validated fix, workaround, or affected-version list.

No specific filenames, hashes, registry artifacts, command lines, or network indicators have been published for BigDiskBuster. Hunting should therefore focus on behavioral signals: a sudden loss of Defender updates combined with unexplained local execution.

The PoC’s current instability limits confidence in its operation, not in the underlying defensive concern. Until Microsoft provides technical guidance, organizations should treat unexplained Defender update failures as a potential security event rather than routine maintenance noise.