CVE-2026-77488 in SQL Server
Summary
by MITRE • 09/09/2026
Integer underflow (wrap or wraparound) in SQL Server allows an authorized attacker to disclose information locally.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described constitutes a critical integer underflow condition within the Microsoft SQL Server database management system, specifically affecting how memory allocation and buffer handling are processed during specific operations. This flaw arises from improper validation of numeric inputs or internal calculations where a subtraction operation results in a negative value that is then interpreted as an extremely large positive unsigned integer due to two's complement arithmetic rules. In the context of SQL Server, such miscalculations often occur when processing complex queries involving large datasets, specific data types like binary strings or varbinary columns, or during internal memory management routines responsible for allocating buffers for query execution plans and result sets. The root cause lies in the failure to check whether a computed size value is valid before passing it to lower-level system calls that allocate heap memory based on this erroneous magnitude.
From an operational perspective, while the initial description indicates local information disclosure by authorized users, the technical reality of integer underflows often extends beyond simple data leakage. When SQL Server allocates a buffer based on a wrapped-around size value, it may write data to memory locations adjacent to the intended buffer boundary if subsequent operations assume standard bounds checking that was bypassed or miscalculated due to the initial error. This can lead to heap corruption, which is frequently exploitable for remote code execution by attackers who have gained access to the database engine through legitimate credentials. The presence of this vulnerability significantly undermines the integrity and availability of the SQL Server instance, as memory corruption can cause service crashes leading to denial of service conditions or allow privilege escalation if combined with other vulnerabilities in the operating system layer.
This flaw aligns closely with Common Weakness Enumeration category CWE-192, which defines integer coercion errors where a value is converted from one numeric type to another without proper range checking, and CWE-682, incorrect calculation of size or quantity leading to buffer overflows or underflows. In the context of the MITRE ATT&CK framework, this vulnerability facilitates techniques related to Initial Access via valid accounts if used for information gathering, but more critically enables Defense Evasion through memory corruption that may bypass security monitoring tools designed to detect standard injection patterns. It also relates to Privilege Escalation vectors where heap exploitation allows an attacker to gain higher-level system permissions than originally granted by the database configuration.
Mitigation strategies must prioritize immediate patching using the latest cumulative updates provided by Microsoft, which address these specific arithmetic validation flaws within the SQL Server engine components. Administrators should enforce strict least-privilege principles for all database accounts, ensuring that no user possesses sysadmin or high-level privileges unless absolutely necessary, thereby limiting the potential impact of any successful exploitation attempt to a local scope rather than allowing full system compromise. Additionally, implementing network segmentation and restricting direct access to SQL Server ports from untrusted networks reduces the attack surface available to internal threat actors who might leverage this vulnerability for lateral movement within an enterprise environment. Regular auditing of query patterns that involve large binary data or complex aggregations can also help in identifying anomalous behavior indicative of exploitation attempts before they result in system instability or data exposure.