CVE-2026-98819 Overview
CVE-2026-98819 is a Linux kernel vulnerability in the Bluetooth btintel driver. The flaw involves improper validation of Device Driver Configuration (DDC) record lengths during firmware parsing. Signed storage of record lengths allowed the value 0xFF to wrap, bypassing size checks before an Intel_Write_DDC command was issued. The upstream fix parses DDC record lengths in unsigned storage and rejects records smaller than the mandatory three-byte header, records exceeding U8_MAX, and records exceeding remaining firmware bytes. The issue was reported by Claude Mythos and resolved across multiple stable kernel branches.
Critical Impact
Malformed DDC records in Intel Bluetooth firmware images can cause out-of-bounds reads or memory corruption in the kernel during device initialization.
Affected Products
- Linux kernel Bluetooth subsystem (drivers/bluetooth/btintel.c)
- Systems using Intel Bluetooth controllers that load DDC firmware records
- Multiple stable kernel branches patched via commits 069031f, 7df748a, b0fce76, c9c15d4, and f361736
Discovery Timeline
- Vulnerability reported by Claude Mythos
- 2026-10-18 - CVE-2026-98819 published to NVD
- 2026-10-21 - Last updated in NVD database
Technical Details for CVE-2026-98819
Vulnerability Analysis
The btintel driver parses DDC firmware records to configure Intel Bluetooth controllers. Each record carries a length byte followed by payload data, and the driver issues an Intel_Write_DDC HCI command with the parsed contents. The pre-patch code stored the record length in a signed variable, which permitted a value of 0xFF to be interpreted as a negative number. This sign-extension behavior caused length comparisons against the remaining firmware buffer to produce incorrect results.
The driver also lacked explicit checks for records smaller than the three-byte mandatory header and records whose declared size exceeded the firmware bytes still available. As a result, parsing a crafted or corrupted firmware image could lead the driver to read beyond the firmware buffer, potentially corrupting kernel memory or triggering a crash during Bluetooth adapter initialization.
Root Cause
The root cause is an input validation error combined with a numeric sign-extension issue [CWE-190, CWE-1284]. The length field was parsed into signed storage, allowing 0xFF to wrap into a negative value. Missing lower-bound and upper-bound checks compounded the issue by not enforcing the mandatory three-byte header, the U8_MAX upper bound, or the remaining firmware size.
Attack Vector
Exploitation requires loading a malicious or malformed DDC firmware blob into the kernel through the Intel Bluetooth driver. This typically requires local privileges sufficient to replace firmware files in /lib/firmware or physical access to supply crafted firmware. Remote exploitation is not a realistic vector because the vulnerable parser consumes firmware images loaded by the kernel at adapter initialization, not data received over the Bluetooth air interface.
The vulnerability manifests when the driver iterates DDC records during btintel initialization. Refer to the kernel patch commits for the exact parser changes and bounds enforcement logic.
Detection Methods for CVE-2026-98819
Indicators of Compromise
- Unexpected kernel oops, warnings, or stack traces referencing btintel, btintel_send_intel_write_ddc, or related firmware parsing functions.
- Bluetooth adapter failing to initialize with error messages referencing malformed DDC records.
- Unauthorized modifications to Intel Bluetooth firmware files under /lib/firmware/intel/.
Detection Strategies
- Monitor dmesg and journal output for btintel parser errors or kernel panics during Bluetooth initialization.
- Audit integrity of firmware blobs in /lib/firmware/intel/ against vendor-supplied hashes.
- Compare running kernel versions against the fixed commits (069031f, 7df748a, b0fce76, c9c15d4, f361736) to identify unpatched hosts.
Monitoring Recommendations
- Enable file integrity monitoring on /lib/firmware to detect unauthorized firmware changes.
- Collect kernel ring buffer logs centrally and alert on btintel or Bluetooth subsystem crashes.
- Track package updates for the kernel across the fleet to confirm patch coverage.
How to Mitigate CVE-2026-98819
Immediate Actions Required
- Update the Linux kernel to a version containing one of the fix commits: 069031f, 7df748a, b0fce76, c9c15d4, or f361736.
- Verify the integrity of Intel Bluetooth firmware files and restore vendor-signed copies if tampering is suspected.
- Restrict write access to /lib/firmware to root only and monitor changes.
Patch Information
The fix is available upstream in the Linux kernel stable tree. See the kernel patches: Kernel Patch 069031f, Kernel Patch 7df748a, Kernel Patch b0fce76, Kernel Patch c9c15d4, and Kernel Patch f361736. Install the kernel update from your Linux distribution once it ships the backport.
Workarounds
- Blacklist the btintel kernel module on systems that do not require Intel Bluetooth functionality using modprobe configuration.
- Disable Bluetooth hardware in firmware or UEFI settings where feasible.
- Enforce strict file permissions on /lib/firmware and use IMA or dm-verity to prevent unauthorized firmware substitution.
# Blacklist the btintel driver until the kernel is patched
echo "blacklist btintel" | sudo tee /etc/modprobe.d/blacklist-btintel.conf
sudo update-initramfs -u
# Verify after reboot
lsmod | grep btintel
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
