CVE-2026-89826 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/panthor: harden firmware build-info bounds checks
panthor_fw_read_build_info() checks whether the metadata range fits in the firmware image with hdr.meta_start + hdr.meta_size. Both fields are u32, so the addition can wrap and let an out-of-bounds range pass validation.
The function also reads the "git_sha: " prefix without first checking that the metadata is long enough, and meta_size == 0 can underflow the NULL terminator index.
Use subtraction-based bounds checking and reject metadata that is too short to contain the expected prefix and trailing NULL byte.
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Analysis
by VulDB Data Team • 09/16/2026
The Linux kernel driver for ARM's Panthor GPU contains a critical integer overflow vulnerability within the firmware build information parsing logic, specifically in the panthor_fw_read_build_info function. This flaw arises from the use of unsigned 32-bit integers to calculate metadata boundaries without adequate protection against arithmetic wraparound. When the sum of the meta_start and meta_size fields exceeds the maximum value representable by a u32 variable, it wraps around to a small positive number rather than triggering an error condition. Consequently, this integer overflow allows out-of-bounds memory ranges to pass validation checks that are designed to prevent buffer overflows or unauthorized access beyond the allocated firmware image boundaries. This type of vulnerability is classically categorized under CWE-190 Integer Overflow or Wraparound and represents a significant risk as it undermines the fundamental assumptions made by subsequent security controls regarding data integrity and boundary enforcement.
Beyond the arithmetic overflow, the implementation exhibits additional logic errors related to insufficient length validation prior to memory access operations. The function attempts to read a specific string prefix labeled git_sha without first verifying that the available metadata buffer is sufficiently large to contain this sequence of characters. Furthermore, if the meta_size field is zero or otherwise malformed such that it underflows when used as an index for locating a NULL terminator, the code may attempt to access memory at invalid addresses. These issues collectively fall under CWE-134 Use of Externally-Controlled Format String and CWE-787 Out-of-bounds Write if the subsequent processing writes data based on these corrupted indices. The lack of rigorous pre-condition checks creates a scenario where malformed or maliciously crafted firmware images can trigger undefined behavior, potentially leading to kernel panics, information disclosure through memory leaks, or arbitrary code execution depending on how the attacker controls the input parameters and what lies adjacent in memory.
The operational impact of this vulnerability is severe due to its location within the graphics subsystem which often operates with elevated privileges relative to user-space applications. An unprivileged local user who can interact with the GPU driver interface may be able to supply a specially crafted firmware blob that exploits these bounds checking failures. Successful exploitation could allow the attacker to read sensitive kernel memory, potentially exposing cryptographic keys or other confidential data stored in adjacent buffers. Alternatively, if the vulnerability leads to a write operation via the corrupted index, it could result in arbitrary code execution with root privileges, effectively compromising the entire system integrity. This aligns with MITRE ATT&CK technique T1059 Command and Scripting Interpreter for initial access or lateral movement scenarios where kernel exploits are used to escalate privileges from user level to system level, bypassing standard security boundaries enforced by the operating system.
To mitigate this vulnerability, it is essential to implement subtraction-based bounds checking rather than relying on addition operations that are susceptible to overflow. Specifically, instead of verifying if meta_start plus meta_size fits within a limit, one should verify if meta_size exceeds the remaining space available from meta_start onward using safe arithmetic comparisons such as ensuring meta_size does not exceed buffer_end minus meta_start. Additionally, strict validation must be applied before any string parsing operations occur; the code must explicitly check that the metadata length is greater than or equal to the size of the expected prefix plus one byte for the NULL terminator. By rejecting metadata structures that are too short early in the processing pipeline, the driver prevents subsequent out-of-bounds reads and potential underflows associated with index calculations. These fixes ensure robust defense-in-depth strategies against malformed inputs and align with secure coding practices recommended by industry standards to prevent integer-related memory corruption vulnerabilities.