CVE-2026-89879 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
media: s2255: bound JPEG frame size before copying into the buffer
s2255_fillbuff() memcpy()s vc->jpg_size bytes of a captured JPEG/MJPEG frame into the vb2 plane. vc->jpg_size is taken verbatim from the S2255_MARKER_FRAME header the device sends (pdword[4] in save_frame())
and, unlike the frame payload length just above it, is never bounded:
payload = le32_to_cpu(pdword[3]);
if (payload > vc->req_image_size) /* payload is checked ... */ return -EINVAL; vc->pkt_size = payload; vc->jpg_size = le32_to_cpu(pdword[4]); /* ... jpg_size is not */
A malicious or malfunctioning device can therefore report a jpg_size larger than the destination vb2 plane, and the memcpy() writes past it. jpg_size is a signed int, so a value with the top bit set also turns into a huge length.
Reject a frame whose jpg_size is negative or exceeds the plane size before copying it.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel media subsystem contains a critical buffer overflow vulnerability within the s2255 driver that allows for arbitrary memory writes when processing JPEG and MJPEG frames from hardware devices. This flaw resides in the s2255_fillbuff function, which is responsible for transferring captured image data into user-space buffers managed by the vb2 framework. The root cause of this issue stems from an asymmetry in input validation logic during frame parsing. While the driver correctly validates the payload length against the requested image size to prevent overflows there, it fails to apply similar bounds checking to the jpg_size field extracted directly from the S2255_MARKER_FRAME header sent by the device hardware. This unchecked value is used as the byte count for a memcpy operation that writes data into a pre-allocated vb2 plane buffer without verifying whether the size fits within the allocated memory region.
From a technical perspective, this vulnerability represents an out-of-bounds write resulting from insufficient validation of external input values derived from untrusted hardware sources. The device firmware or malicious peripheral can supply a jpg_size value that exceeds the dimensions of the destination buffer. Because jpg_size is implemented as a signed integer, it introduces additional risk through potential sign extension issues; if the most significant bit is set, the value may be interpreted as negative by the kernel memory copy routine. Depending on how the underlying memcpy implementation handles length parameters or subsequent logic checks, this can lead to either immediate buffer overflows with positive oversized values or undefined behavior and further corruption when handling large unsigned integers cast to signed types. This lack of boundary enforcement violates fundamental principles of secure coding where all inputs from external interfaces must be strictly validated against expected constraints before use in memory operations.
The operational impact of this vulnerability is severe, as it enables local privilege escalation and system instability through arbitrary kernel memory modification. An attacker with access to the device node can craft a malicious JPEG stream or exploit a malfunctioning hardware component to trigger the out-of-bounds write. By carefully controlling the jpg_size value, an adversary can overwrite adjacent kernel structures, potentially gaining control over execution flow via function pointer corruption or achieving code execution in ring zero privileges. This compromises the integrity and confidentiality of the entire system, allowing for data exfiltration, denial of service through kernel panics, or further exploitation chains targeting other subsystems that may be affected by memory layout changes caused by the overflow.
This vulnerability aligns with CWE-120 Buffer Copy without Checking Size of Input Classic buffer overflow and CWE-787 Out-of-bounds Write in terms of classification. In the context of attack tactics, it relates to ATT&CK technique T1059 Command and Scripting Interpreter if used for initial access via crafted media files, but more critically maps to privilege escalation vectors where kernel memory corruption is leveraged to bypass security boundaries. The failure to validate hardware-provided metadata against buffer limits reflects a common pattern in embedded driver development where trust in device compliance leads to insufficient defensive coding practices.
Mitigation requires immediate patching of the s2255 driver to enforce strict bounds checking on all size fields derived from device headers before they are used in memory operations. Specifically, developers must validate that jpg_size is positive and does not exceed the allocated plane size prior to invoking memcpy. Additionally, input validation should be applied consistently across all similar drivers handling multimedia streams to prevent recurrence of this class of vulnerabilities. System administrators should ensure their kernels are updated with upstream fixes addressing this specific issue in the media subsystem. Long-term remediation involves adopting static analysis tools and fuzzing frameworks that specifically target kernel memory safety issues during driver development cycles, ensuring that all external inputs from hardware interfaces undergo rigorous validation against defined constraints before being processed by sensitive system functions.