CVE-2026-89879: Linux Kernel s2255 Buffer Overflow Vulnerability

CVE-2026-89879 Overview

CVE-2026-89879 is a Linux kernel vulnerability in the s2255 media driver that allows an out-of-bounds write when handling JPEG/MJPEG frames from a USB video capture device. The s2255_fillbuff() function copies vc->jpg_size bytes from a captured frame into a vb2 plane buffer without validating that the size fits within the destination. The jpg_size value is taken directly from the device-supplied S2255_MARKER_FRAME header. A malicious or malfunctioning device can report a size larger than the plane or a negative signed value, causing memcpy() to write past the destination buffer.

Critical Impact
A crafted or malfunctioning USB device attached to a Linux host running the s2255 driver can trigger a kernel heap out-of-bounds write, leading to memory corruption, denial of service, or potential privilege escalation.

Affected Products

Linux kernel builds including the s2255 (Sensoray 2255) V4L2 media driver
Distributions shipping vulnerable kernel versions prior to the fix commits listed by upstream
Systems permitting attachment of USB video capture devices bound to the s2255 driver

Discovery Timeline

2026-09-16 - CVE-2026-89879 published to NVD
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-89879

Vulnerability Analysis

The defect resides in the Sensoray 2255 USB video capture driver (drivers/media/usb/s2255/s2255drv.c). During frame reassembly, save_frame() parses the marker header sent by the device and extracts two length fields: the frame payload at pdword[3] and the JPEG frame length jpg_size at pdword[4]. The driver validates payload against vc->req_image_size and returns -EINVAL when it exceeds the limit, but performs no comparable check on jpg_size.

Later, s2255_fillbuff() invokes memcpy() using vc->jpg_size as the length argument, copying frame bytes into the videobuf2 plane. Because jpg_size is device-controlled and unchecked, the copy can extend beyond the destination allocation.

Root Cause

The root cause is missing input validation on an attacker-influenced length field prior to a memory copy, a classic Out-of-Bounds Write ([CWE-787]). Compounding the issue, jpg_size is declared as a signed int. A value with the high bit set is interpreted as a negative number in signed comparisons but is implicitly converted to a very large size_t when passed to memcpy(), defeating naive bounds checks and producing a large write length.

Attack Vector

Exploitation requires the target host to bind the s2255 driver to a USB video device. The attacker supplies a crafted device — either physical hardware, a programmable USB emulator, or a compromised peripheral — that emits an S2255_MARKER_FRAME header specifying a jpg_size larger than the allocated vb2 plane. When the kernel processes the frame, the driver copies attacker-supplied bytes past the buffer boundary, corrupting adjacent kernel heap memory.

The upstream fix rejects any frame whose jpg_size is negative or exceeds the destination plane size before the copy occurs. See the upstream kernel commit for the corrected validation logic.

Detection Methods for CVE-2026-89879

Indicators of Compromise

Kernel oops, panic, or SLUB/SLAB corruption messages referencing s2255_fillbuff, save_frame, or videobuf2 allocations
KASAN reports flagging out-of-bounds writes in the s2255 driver call path
Unexpected USB device enumerations binding to the s2255 driver on hosts without legitimate Sensoray hardware

Detection Strategies

Enumerate running kernel versions and compare against the fixed commits listed in the kernel.org stable tree
Audit lsmod output and /sys/bus/usb/drivers/s2255/ bindings across the fleet to identify hosts loading the vulnerable driver
Enable KASAN in test builds to surface out-of-bounds writes triggered by fuzzed USB input

Monitoring Recommendations

Forward dmesg and journald kernel logs to a centralized analytics tier and alert on driver-scoped oops and KASAN traces
Monitor USB device connection events on servers, kiosks, and workstations for unexpected video-class devices
Track kernel package versions on Linux endpoints and flag hosts running unpatched builds

How to Mitigate CVE-2026-89879

Immediate Actions Required

Update to a Linux kernel version that includes the fix commits published on git.kernel.org (e504cc88, dd739517, d2ecaaab, 79f58f90, 68d664f1, 4b6f7bbc, 32a595dd, 2542516a)
On systems that do not require Sensoray 2255 hardware, blacklist the s2255 module to eliminate the attack surface
Enforce USB device control policies on hosts where physical access is possible

Patch Information

Upstream Linux maintainers merged fixes across multiple stable branches. The corrected s2255_fillbuff() path validates jpg_size against the destination plane size and rejects negative values before invoking memcpy(). Reference commits include 2542516a, 32a595dd, 4b6f7bbc, 68d664f1, 79f58f90, d2ecaaab, dd739517, and e504cc88.

Workarounds

Blacklist the s2255 kernel module on hosts that do not use Sensoray 2255 capture hardware
Restrict USB device attachment through hardware controls, USBGuard policies, or kernel usbcore.authorized_default=0 settings
Limit physical access to systems that must retain the driver enabled

bash

# Blacklist the vulnerable driver until the kernel is patched
echo "blacklist s2255" | sudo tee /etc/modprobe.d/blacklist-s2255.conf
sudo rmmod s2255 2>/dev/null || true
sudo update-initramfs -u

# Optionally deny new USB devices by default (requires per-device authorization)
echo 0 | sudo tee /sys/bus/usb/devices/usb*/authorized_default