CVE-2026-89818 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu/vcn: fix integer overflow in dec_msg buffer count check
If the supplied msg[2] (num_buffers) is 0x3FFFFFFF, the expression
6 + num_buffers * 4 wraps to 2 and the bounds check passes, letting the parser loop far past the end of the message BO. Triggering it additionally requires a ~4GiB mapping so that msg[1] survives the
earlier "header does not fit in BO" check.
Rewrite the test in division form, which is overflow-free by construction. Also update the message to reflect that msg is invalid.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 09/16/2026
The Linux kernel's AMD GPU driver contains a critical integer overflow vulnerability within the Video Coding Engine (VCE) command parser, specifically located in the buffer count validation logic for decode messages. This flaw arises from an arithmetic operation used to calculate the total size of a message structure before validating it against the allocated buffer object limits. The specific calculation involves adding six bytes to four times the value provided by msg[2], which represents the number of buffers requested by user-space applications. When this input is set to 0x3FFFFFFF, the multiplication operation results in an integer overflow because the product exceeds the maximum limit for a signed 32-bit integer. Consequently, the result wraps around to a small positive value, specifically two bytes, which passes the subsequent bounds check that verifies if the calculated size fits within the allocated buffer object.
This arithmetic error allows malicious or buggy user-space applications to bypass security checks designed to prevent out-of-bounds memory access. By exploiting this condition, an attacker can cause the parser loop to iterate far beyond the intended end of the message buffer object. The exploitation requires a specific precondition where approximately four gigabytes of virtual address space are mapped so that msg[1] survives earlier header validation checks. Once these conditions are met, the kernel proceeds to process data from memory locations outside the bounds of the allocated buffer. This leads to an out-of-bounds read operation, which can result in information disclosure if sensitive kernel or user-space data is leaked through the malformed message processing path. In more severe scenarios involving subsequent write operations triggered by similar logic flaws, this could potentially lead to arbitrary code execution with kernel privileges.
From a classification perspective, this vulnerability aligns with CWE-190, which describes integer overflow or wraparound resulting in an incorrect value that leads to security weaknesses such as buffer overflows. The attack vector is classified under ATT&CK technique T1203, specifically the exploitation of vulnerabilities for execution, where attackers leverage software flaws to gain unauthorized access or execute code. The root cause lies in improper validation of numerical inputs before performing arithmetic operations, a common pitfall in systems programming languages like C that do not automatically handle overflow conditions.
The resolution involves rewriting the bounds check test using division instead of multiplication to avoid integer overflow entirely. By dividing the available buffer size by four and comparing it against the number of buffers plus an offset for headers, the validation logic becomes mathematically sound regardless of how large the input value is. This approach ensures that any attempt to specify a massive number of buffers will correctly fail the bounds check rather than wrapping around to pass it. Additionally, the fix updates error handling messages to explicitly indicate invalid message structures, improving diagnostic capabilities for developers and system administrators monitoring kernel logs.
To mitigate this vulnerability in environments where immediate patching is not feasible, strict input validation should be enforced at the user-space API boundary before any data reaches the kernel driver. Limiting the maximum allowable values for buffer counts can prevent overflow conditions from occurring even if the underlying code remains vulnerable. Furthermore, enabling Kernel Address Space Layout Randomization (KASLR) and other memory protection mechanisms such as Stack Canaries and Full RELRO can reduce the exploitability of this flaw by making it harder to predict memory layouts or overwrite critical control data. Regular updates to the Linux kernel are essential to ensure that these low-level driver vulnerabilities are addressed, maintaining the integrity and security of systems relying on AMD GPU hardware acceleration for video processing tasks.