EY 4TB SQL Backup Leak Highlights Cloud Security Gaps

A 4‑terabyte SQL Server backup file belonging to Ernst & Young (EY) was discovered publicly accessible on Microsoft Azure, exposing an unencrypted .BAK backup that researchers say could have contained database schemas, stored procedures, authentication tokens, API keys, service‑account credentials and other high‑value secrets — a misconfiguration that underscores how brittle cloud operational hygiene can be even inside the world’s best‑resourced organizations.

Background​

The exposure was uncovered during routine attack‑surface mapping by researchers at Neo Security. The team’s lead researcher observed an HTTP HEAD response that reported a 4‑terabyte object with a .BAK filename and, after retrieving only the first kilobyte to avoid unlawful download, confirmed it contained the signature of a SQL Server backup and that the file was not encrypted. Neo Security’s public write‑up describes the verification steps (HEAD request, SOA/DNS correlation, sampling the file header) used to determine the risk without downloading more than the minimum metadata needed to confirm format and ownership. Independent outlets corroborated the scale and format of the exposure, reporting the same 4 TB figure and identifying the file as a SQL Server .BAK backup. These outlets characterize the incident as a classic cloud misconfiguration — an Azure Blob access control list (ACL) or container policy that left the backup readable to the public internet.

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What was exposed — why a .BAK matters​

A SQL Server full backup (.BAK) is a point‑in‑time copy of the entire database: schema, tables, stored procedures, and data pages. In most applications these backups contain not only business records but also embedded secrets and artifacts that are priceless to attackers:

• Authentication material: hashed or even plain credentials, cached OAuth tokens, session cookies or refresh tokens.
• System secrets: API keys, third‑party service tokens, connection strings.
• Business logic and trade secrets: SQL stored procedures, application logic, and proprietary queries.
• Personally identifiable information (PII): names, emails, financial identifiers, and other regulated data sets.

Because backups are often taken from production systems and stored as exact snapshots, they can be a single‑file equivalent of an entire application stack. That makes a 4‑TB backup functionally catastrophic if anyone outside a trusted, audited team can read it. Industry reporting repeatedly calls out that even brief public exposure is risky due to the ubiquity of automated scanners and opportunistic bots that index cloud endpoints.

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How the discovery was verified​

Neo Security’s publicly described verification chain contains several common investigative touchpoints that responsibly balance confirmation with legal and ethical limits:

• Passive reconnaissance (HEAD requests) to establish file metadata and size without retrieving content beyond allowed small‑byte samples.
• Header sampling (first 1,000 bytes) to identify magic bytes and format — enough to confirm a SQL Server backup signature and encryption absence.
• Correlation to corporate ownership using DNS SOA records and ancillary artifacts (merger documents, translated text) to attribute the storage account to EY.
• Responsible disclosure attempts to the company’s CSIRT over multiple channels before any public disclosure.

These are standard, defensible steps for third‑party researchers who must avoid copying or exfiltrating sensitive content to demonstrate an issue. The public accounts of the incident reiterate that Neo Security avoided downloading the whole object.

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Verification caveats and what is — and isn’t — public​

Several elements reported in researcher write‑ups and wider coverage are verified by independent media, including the object size (4 TB), the file extension (.BAK), and that the first bytes indicated an unencrypted SQL Server backup. Major tech outlets reported those core facts from the Neo Security disclosure. What is less clear in publicly accessible records is the detailed content of the backup and whether any sensitive client or regulated data was actually present or access‑taken prior to remediation. Multiple news accounts state that Neo Security contacted EY and that EY remediated the exposure, with some reports saying EY confirmed no client or confidential data had been affected. However, at the time of writing there was no independently verifiable press release or public statement on ey.com that details the forensic outcome or provides a full scope statement; that absence of a posted, authoritative public statement should be treated as a caution when interpreting third‑party summaries. Where reporters cite direct confirmation from EY, the underlying primary statement appears to have been through coordinated disclosure channels rather than a public web post. Readers should treat any claim about “no data affected” as contingent until an audited, documented disclosure is produced by the company or an independent forensic report is published. This qualification is important because public assertions made during incident response often evolve following forensic review.

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Technical anatomy: why cloud backups go public​

This incident is a textbook case of a handful of recurring, well‑known failure modes:

• Misconfigured container ACLs: Azure Blob containers and $web static endpoints can be left with anonymous read access by mistake. Static website endpoints in particular can be public even if container ACLs are changed later.
• SAS token misuse: Long‑lived or overly permissive Shared Access Signatures (SAS) are easy to create and easy to leak, especially when embedded in scripts or automation.
• Credential leakage in CI/CD: DevOps pipelines that commit credentials, keys, or connection strings to public repos or artifacts open a direct path for attackers to create their own access.
• Lack of backup encryption or TDE at rest: Backups created without database‑level encryption (for example, Transparent Data Encryption or explicit backup encryption with keys from Azure Key Vault) will appear as readable .BAK files to anyone who downloads them.
• Insufficient detection and centralized visibility: Large estates commonly lack continuous discovery for public blobs or misconfigurations; scanning and leak detection must be automated.

Microsoft’s operational guidance and enterprise advisories emphasize the same controls — Defender for Storage, Private Link and firewall rules, short‑lived SAS tokens, and backup encryption using Azure Key Vault or TDE to protect backups and reduce the blast radius of any accidental exposure. Microsoft documentation also details encrypting backups using asymmetric keys stored in Key Vault and using TDE to ensure both data files and backups are encrypted at rest.

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Why automated scanning makes exposures effectively immediate threats​

Attackers and benign scanners alike enumerate cloud storage endpoints at scale. Automated tooling can discover and index misconfigured storage in minutes. That means accidental public exposures typically become discoverable almost immediately, and the relevant questions are not “if” a human adversary will find the object, but how many automated actors indexed or copied it before remediation. Neo Security and other observers highlight historical incidents where brief five‑minute exposures were sufficient for attackers to harvest credentials and escalate to full breaches and ransomware. The lesson is simple: at cloud scale, human speed cannot outpace automated reconnaissance.

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Response timeline and disclosure — what we can reasonably say​

Public reporting recounts that Neo Security attempted responsible disclosure, reached EY’s security team, and that EY remediated the storage account and removed public access within about a week of being contacted. Neo Security’s write‑up praised EY’s CSIRT for a professional response. Independent reports echo the same characterizations. However, the timing and scope language in public news stories is derived from Neo Security’s report and interview exchanges; there is no traceable, publicly archived EY press release with a full forensic timeline at the time this article was published. Consequently, while the containment action is widely reported, the final forensic conclusions remain under the company’s control until a public disclosure is posted. Readers should therefore treat the remediation claims as credible but subject to confirmation via an EY published post‑incident report or independent audit.

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The real risks that come from a backup like this​

• Credential harvesting and lateral movement: If the backup contained API keys, service account credentials, or OAuth tokens, an attacker could pivot to other assets, spin up cloud instances, or move laterally across tenant boundaries.
• Supply‑chain and client impact: EY’s client base includes highly sensitive enterprises; leaked client data or secrets can enable fraud, market manipulation or targeted attacks against those downstream organizations.
• Model poisoning and long‑term abuse: Large archives of business or telemetry data can be repurposed as training data for models or weaponized to craft hyper‑targeted phishing and social‑engineering campaigns.
• Regulatory and contractual fallout: Exposure of PII or regulated data could trigger notification obligations under data protection laws, auditor scrutiny, or client contract penalties.
• Irreversible exfiltration: Once data is copied off the cloud tenant by unknown actors, revocation and containment cannot retrieve that material. The only mitigations are detection, rotation (keys/passwords), and legal/forensic remedies.

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Verification of defensive mitigations and best practices​

Multiple vendor and Microsoft guidance documents confirm practical, implementable mitigations:

• Encrypt backups at creation time: Use SQL Server backup encryption with a key managed in Azure Key Vault or enable Transparent Data Encryption (TDE) and ensure backups are created with encryption parameters so a downloaded .BAK file remains unreadable without the key. Microsoft documentation provides explicit T‑SQL patterns and Key‑Vault integration steps for both TDE and backup encryption.
• Lock down storage network access: Use Private Link/private endpoints and storage firewalls to limit which networks and principals can reach blob endpoints. Avoid exposing backups through static website hosting.
• Short‑lived and minimal SAS tokens: Replace long‑lived account keys with scoped, short‑lived SAS tokens or managed‑identity flows. Monitor for mass SAS issuance.
• Enable Defender for Storage and sensitive‑data detection: On‑upload scanning and sensitive‑data classification can automate quarantining or tagging of risky artifacts and integrate with SIEM playbooks for fast response. Defender for Storage also emits the signals defenders need to detect mass copy activity or anomalous StartCopy/AzCopy jobs.
• Immutability and separate control planes for backups: Hold immutable snapshots and backup copies in separate subscriptions or control planes so that a single tenant compromise cannot trivially delete all recovery points.
• Pipeline hygiene: Treat incoming data as untrusted, place ingestion into shielded quarantine accounts, require “scan‑clean” tags before pipelines consume objects, and integrate malware scanning at the DMZ tier.

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Practical step‑by‑step remediation checklist for organizations running SQL Server on Azure​

• Immediately audit all storage accounts for containers with anonymous read or public ACLs; close or restrict public access.
• Rotate any long‑lived storage account keys and revoke any SAS tokens that were generated around the time of the exposure.
• If backups were created without encryption, assume secrets could be recovered and rotate exposed credentials, service keys, and certificates.
• Enable backup encryption and TDE for production databases; store keys in Azure Key Vault with strict access controls.
• Enable Defender for Storage’s sensitive‑data threat detection and on‑upload malware scanning for ingestion endpoints.
• Snapshot and preserve forensic images of the exposed container and access logs before remediation for legal and investigative needs.
• Engage independent forensics to determine whether data was accessed, copied or exfiltrated. If so, implement notification plans required by law or contractual obligations.
• Harden CI/CD and secret handling practices: move secrets to Key Vault, use managed identities, and implement pre‑commit secret scanning.

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Strengths and weaknesses observed in this incident​

Strengths:

• The discovery followed responsible‑disclosure norms: minimal data sampled, multiple contact attempts, and escalation to CSIRT rather than public dumping. Reporting praised the responsible behavior of the researcher.
• The quick remediation (as reported) indicates a functional incident response capability within EY’s security organization.

Weaknesses:

• The existence of an unencrypted 4‑TB backup in a public container points to systemic control gaps: poor backup encryption policy enforcement, lack of automated discovery for public blobs, and likely insufficient pipeline validation that would stop backups from being staged in public containers.
• Public assertions of “no client data impacted” without a posted forensic report or auditor‑verified statement remain unverifiable in the absence of a formal disclosure document. This lack of a public, auditable statement is a common friction point for regulators and customers who demand evidence.

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Strategic lessons for enterprise cloud security teams​

• Assume the worst‑case for any public object: automated scanning makes exposures effectively immediate. Assume any public blob has been observed and act accordingly (rotate keys, revoke secrets, notify).
• Treat backups as high‑value crown jewels: backups should follow stricter handling policies than routine artifacts: encryption by default, access policies, immutability, and separate control planes are non‑negotiable.
• Operationalize detection, not just prevention: CSPM (cloud security posture management), Defender for Storage, and automated hunting playbooks are necessary because human review will always lag automated reconnaissance.
• Reduce blast radius with keys in Key Vault and short‑lived tokens: never bake long‑lived credentials into scripts or images that could leak.
• Make recovery plans defensive: assume exfiltration and prioritize rotation and remediation over containment alone.

These are not theoretical. Microsoft’s own guidance maps to these controls and the community post‑incident playbooks reflect the same priorities: least privilege, encryption, network isolation, and automated detection.

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Conclusion​

The discovery of a 4‑terabyte unencrypted SQL Server backup tied to Ernst & Young — whether the exposure was brief or extended — is a stark reminder that cloud convenience and the velocity of modern operations can create catastrophic lapses in basic controls. Large‑scale automated scanners turn what used to be human‑scale mistakes into immediate, enterprise‑scale threats. The technical remedies are well understood — backup encryption, Key Vault key management, least‑privilege SAS usage, private endpoints, and continuous automated posture monitoring — yet they are still not universally applied where human processes and convenience drive decisions.
This incident should push organizations to treat backups as first‑class security assets, to automate continuous discovery and response, and to insist on audit‑grade post‑incident disclosures so customers, regulators and partners can verify mitigation outcomes. Until those operational practices are habitual across large cloud estates, the same pattern of high‑impact exposures will repeat.

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Source: Security Affairs Ernst & Young Exposes 4TB SQL Server Backup Publicly on Microsoft Azure