CVE-2026-98830: Linux Kernel WFX Buffer Overflow Vulnerability

CVE-2026-98830 Overview

CVE-2026-98830 is an out-of-bounds read vulnerability in the Linux kernel's Silicon Labs wfx WiFi driver. The flaw resides in the wfx_hif_read_mib() function, which copies reply->length bytes from a firmware response into a caller-provided buffer without validating that reply->length does not exceed val_len. A malicious or malformed firmware response with an oversized length field can overrun the caller buffer and read past the end of the reply allocation. The Linux kernel maintainers resolved the issue by replacing a dead -ENOMEM check with active validation of reply->length before the memcpy call.

Critical Impact
A crafted firmware Management Information Base (MIB) response can trigger kernel memory corruption or disclosure through an unchecked memcpy in the WiFi driver read path.

Affected Products

Linux kernel versions containing the wfx WiFi driver prior to the fix commits
Systems using Silicon Labs WF200 series WiFi modules via the wfx driver
Stable kernel branches referenced in the upstream fixes (02886c18, 71d14009, 7acb36fd, 819d4c13, ce67ebe9)

Discovery Timeline

2026-10-18 - CVE-2026-98830 published to NVD
2026-10-21 - Last updated in NVD database

Technical Details for CVE-2026-98830

Vulnerability Analysis

The wfx_hif_read_mib() function in the Linux kernel wfx WiFi driver issues a Host Interface (HIF) request to the WF200 firmware to read a MIB object. The firmware returns a reply structure containing a length field and the requested data payload. The driver then calls memcpy to transfer reply->length bytes into a buffer supplied by the caller, whose capacity is tracked by val_len.

Before the fix, the driver trusted the firmware-supplied reply->length value and did not compare it against the caller buffer size. A reply that claims a length larger than val_len causes memcpy to write past the end of the caller buffer. The same oversized length also causes the driver to read past the end of the reply allocation that the HIF layer prepared.

The original code included an -ENOMEM branch that was unreachable, providing no runtime protection. The upstream patch removes the dead check and adds an active comparison that returns an error when reply->length exceeds val_len, preventing the unsafe copy.

Root Cause

The root cause is missing input validation on a length field received from an external component (the WiFi firmware) before it is used as the size argument to memcpy. This is a classic buffer overflow and out-of-bounds read pattern [CWE-120, CWE-125] where a trust boundary between kernel driver and device firmware is crossed without bounds checking.

Attack Vector

Exploitation requires that the attacker influence the content of HIF replies returned by the WF200 firmware. Realistic paths include a compromised or tampered firmware image, a malicious device impersonating the WF200 on the host bus, or supply-chain modification of firmware files loaded at driver initialization. The vulnerability triggers in kernel context during normal MIB read operations invoked by the WiFi stack.

No verified public exploit code is available. The vulnerability is described in the upstream commit messages for the referenced kernel git changes. See the Kernel Git Change 02886c18 commit for the patch content.

Detection Methods for CVE-2026-98830

Indicators of Compromise

Unexpected kernel oops, panic, or KASAN splats originating in wfx_hif_read_mib or neighboring wfx driver symbols
Unexplained WiFi driver reinitialization or firmware reload events in dmesg
Checksum mismatches on wfm_wf200_*.sec firmware files compared to vendor-published hashes

Detection Strategies

Enable CONFIG_KASAN on test and development kernels to surface the out-of-bounds read when loading potentially malicious firmware
Audit kernel version and wfx driver source against the fix commits (02886c18, 71d14009, 7acb36fd, 819d4c13, ce67ebe9)
Monitor loaded firmware blobs under /lib/firmware/ for unauthorized modification using file-integrity monitoring

Monitoring Recommendations

Forward kernel ring buffer and journald logs to a centralized log platform and alert on wfx subsystem errors
Track hardware inventory of devices using the Silicon Labs WF200 module to scope affected endpoints
Correlate driver crash events with recent firmware deployment or OTA update activity

How to Mitigate CVE-2026-98830

Immediate Actions Required

Update affected Linux systems to a kernel release that includes the upstream fix commits referenced in the NVD advisory
Verify integrity of wfx firmware images against vendor-supplied hashes before deployment
Restrict physical and bus-level access to devices that embed the WF200 WiFi module

Patch Information

The fix replaces the unreachable -ENOMEM check in wfx_hif_read_mib() with an active validation that reply->length fits within val_len before the memcpy. Patches are available in the stable kernel tree via commits 02886c18, 71d14009, 7acb36fd, 819d4c13, and ce67ebe9. Refer to the Kernel Git Change 71d14009 and Kernel Git Change 7acb36fd entries for the backported variants.

Workarounds

Unload the wfx kernel module on systems that do not require the WF200 WiFi module until a patched kernel is deployed
Blacklist the wfx driver via /etc/modprobe.d/ on hosts where the hardware is unused
Apply file-integrity controls to the firmware directory to detect unauthorized modification of wfx firmware blobs

bash

# Prevent the wfx driver from loading until the kernel is patched
echo 'blacklist wfx' | sudo tee /etc/modprobe.d/blacklist-wfx.conf
sudo modprobe -r wfx 2>/dev/null || true
sudo update-initramfs -u