CVE-2026-77482: SQL Server RCE Vulnerability

CVE-2026-77482 Overview

CVE-2026-77482 is a heap-based buffer overflow vulnerability in Microsoft SQL Server. An unauthenticated attacker can trigger the flaw over a network and execute arbitrary code in the context of the SQL Server process. The vulnerability is classified under [CWE-122] Heap-based Buffer Overflow. Successful exploitation requires user interaction, based on the CVSS vector.

Microsoft published the advisory through the Microsoft Security Response Center. The flaw affects the confidentiality, integrity, and availability of the database server and any data it holds.

Critical Impact

Remote code execution against SQL Server without prior authentication, exposing hosted databases, credentials, and any downstream systems that trust the database tier.

Affected Products

• Microsoft SQL Server (specific versions listed in the Microsoft Security Update Guide)
• Systems exposing SQL Server endpoints to untrusted networks
• Applications relying on vulnerable SQL Server instances for backend storage

Discovery Timeline

• 2026-09-08 - CVE-2026-77482 published to NVD
• 2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-77482

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow within SQL Server's network-facing processing logic. An attacker who can reach the database service over the network can send crafted input that overflows a heap allocation. The overflow corrupts adjacent heap metadata or object pointers, giving the attacker control over the execution flow of the SQL Server process.

Because the flaw is reachable prior to authentication, exploitation does not require valid credentials. The CVSS vector indicates user interaction is required, which suggests a client-side or administrative action participates in the attack chain. Successful code execution runs with the privileges of the SQL Server service account, which is often highly privileged on the host.

Root Cause

The root cause is improper validation of the size of attacker-controlled data before it is written into a heap buffer inside SQL Server. This class of defect [CWE-122] typically arises when length fields in a network protocol are trusted without bounds checking. Microsoft has not published detailed root-cause internals in the public advisory.

Attack Vector

The attack vector is network-based. An unauthenticated remote attacker sends a malformed request to an exposed SQL Server endpoint. Once user interaction completes the required precondition, the crafted payload triggers the heap overflow and hijacks execution. See the Microsoft Security Update Guide for protocol-level details.

No verified proof-of-concept code is publicly available. The EPSS probability at publication was 0.767%.

Detection Methods for CVE-2026-77482

Indicators of Compromise

• Unexpected crashes or restarts of the sqlservr.exe process, particularly with access violation exceptions in Windows Event Log.
• Anomalous outbound network connections from the SQL Server host to unknown external addresses.
• New or unexpected child processes spawned by the SQL Server service account, such as cmd.exe, powershell.exe, or rundll32.exe.

Detection Strategies

• Monitor SQL Server hosts for process-lineage anomalies where sqlservr.exe becomes the parent of shell or scripting interpreters.
• Inspect network telemetry for malformed TDS (Tabular Data Stream) traffic and unusually large pre-authentication packets to TCP 1433 or configured SQL ports.
• Correlate Windows Error Reporting entries for heap corruption faults in the SQL Server process with inbound network sessions.

Monitoring Recommendations

• Enable and centralize SQL Server error logs, Windows Security and Application logs, and endpoint process telemetry.
• Alert on service crashes followed by service restarts within short time windows on database hosts.
• Baseline normal client connectivity to SQL Server and flag connections from unexpected source networks or geographies.

How to Mitigate CVE-2026-77482

Immediate Actions Required

• Apply the Microsoft security update for CVE-2026-77482 to every affected SQL Server instance as identified in the Microsoft Security Update Guide.
• Restrict network exposure of SQL Server so it is not reachable from untrusted networks or the public internet.
• Audit SQL Server service accounts and reduce their privileges to the minimum required.

Patch Information

Microsoft has released a security update for the affected SQL Server versions. Consult the Microsoft Security Update Guide for the specific build numbers, cumulative updates, and download links applicable to your deployment.

Workarounds

• Place SQL Server behind a firewall and allowlist only trusted application and administrative hosts.
• Require IPsec or VPN tunneling for all SQL Server client connectivity where feasible.
• Disable SQL Browser service and any unused SQL Server network protocols to reduce exposed attack surface.
• Segment database servers into isolated network zones with strict east-west traffic controls.

# Configuration example: restrict SQL Server (TCP 1433) to trusted subnet only
New-NetFirewallRule -DisplayName "SQL Server - Trusted Only" `
  -Direction Inbound -Protocol TCP -LocalPort 1433 `
  -RemoteAddress 10.10.0.0/16 -Action Allow

New-NetFirewallRule -DisplayName "SQL Server - Block All Others" `
  -Direction Inbound -Protocol TCP -LocalPort 1433 `
  -Action Block