CVE-2026-74444 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/vmwgfx: validate DRAW_PRIMITIVES header size before division
vmw_cmd_draw() computes
maxnum = (header->size - sizeof(cmd->body)) / sizeof(*decl);
where header->size is u32 and is taken straight from the user-supplied command stream. When header->size is less than sizeof(cmd->body) the unsigned subtraction wraps to nearly 4 GiB, producing a huge maxnum. Any user-controlled cmd->body.numVertexDecls then passes the bound and the loop dereferences decl[i] far past the end of the kernel command
bounce buffer, producing an out-of-bounds read of kernel memory.
Reject undersized headers up front.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability resides within the vmwgfx driver of the Linux kernel, specifically in the drm/vmwgfx subsystem where graphics command processing occurs. This issue manifests as a classic integer overflow and subsequent out-of-bounds memory access scenario that can be exploited by malicious users to read kernel memory. The flaw exists in the vmw_cmd_draw() function which processes graphics commands from user space, creating a dangerous condition when handling malformed command headers.
The technical implementation of this vulnerability stems from improper validation of input parameters before arithmetic operations. When processing DRAW_PRIMITIVES commands, the driver calculates maxnum using an unsigned 32-bit integer subtraction that does not account for potential underflow conditions. The calculation maxnum = (header->size - sizeof(cmd->body)) / sizeof(*decl) becomes problematic when header->size is smaller than the expected command body size. This condition causes unsigned integer wraparound, resulting in a massive positive value that appears to be nearly 4 gigabytes instead of a negative or zero result.
The operational impact of this vulnerability extends beyond simple memory corruption, as it enables an attacker to perform out-of-bounds reads of kernel memory space through the command stream processing loop. The loop iterates based on the inflated maxnum value and attempts to dereference vertex declaration structures far beyond the allocated bounce buffer boundaries. This creates a potential information disclosure scenario where sensitive kernel data could be accessed and exfiltrated by an unprivileged user, undermining system security and confidentiality.
This vulnerability aligns with CWE-129 Input Validation and CWE-191 Integer Underflow/Overflow categories, representing a fundamental flaw in input sanitization and arithmetic operation validation. The ATT&CK framework would categorize this under T1059 Command and Scripting Interpreter and potentially T1566 Impairing Security Features, as it enables privilege escalation through memory corruption. The mitigation strategy involves implementing upfront validation of command header sizes before any arithmetic calculations, ensuring that undersized headers are rejected immediately rather than allowing the computation to proceed with invalid parameters.
The fix implemented addresses the root cause by rejecting command headers that are smaller than the minimum required size for processing. This defensive programming approach prevents the wraparound condition from ever occurring while maintaining the driver's functionality for legitimate graphics operations. The solution demonstrates proper input validation practices that should be applied across all kernel subsystems handling user-supplied data, particularly in contexts involving memory allocation and arithmetic calculations. This patch exemplifies how simple boundary checks can prevent complex exploitation scenarios and reinforces the principle that kernel code must never trust user-provided data without proper sanitization.
The vulnerability represents a critical security issue in graphics drivers that could be exploited by local users to gain unauthorized access to kernel memory contents, potentially exposing sensitive information such as cryptographic keys, credentials, or system configuration details. The attack surface is particularly concerning given that graphics processing commands are routinely submitted by user applications and may be manipulated through various attack vectors including compromised applications or malicious code injection techniques. Proper validation of all input parameters, especially those derived from user-space command streams, remains essential for maintaining kernel memory safety and preventing similar issues in other subsystems.