CVE-2026-89730 Overview
CVE-2026-89730 is an out-of-bounds read vulnerability in the Linux kernel's Altera CvP (Configuration via Protocol) FPGA driver. The flaw resides in the altera_cvp_send_block() function, which handles bitstream transfers to Altera FPGAs. The trailing byte code path dereferences a u32 pointer even when only 1-3 bytes remain in the input buffer. When the buffer terminates at a page or scatterlist boundary, this read can extend past valid image data and trigger a fault.
Critical Impact
A malformed FPGA bitstream image sized to end near a page or scatterlist boundary can trigger an out-of-bounds read in kernel space, potentially causing a kernel fault and denial of service on systems using Altera CvP FPGA programming.
Affected Products
- Linux kernel with the fpga/altera-cvp driver enabled
- Systems using Altera FPGA devices programmed through the Configuration via Protocol interface
- Distributions shipping kernel builds prior to the fix commits referenced in kernel.org
Discovery Timeline
- 2026-09-11 - CVE-2026-89730 published to NVD
- 2026-09-14 - Last updated in NVD database
Technical Details for CVE-2026-89730
Vulnerability Analysis
The Altera CvP driver streams FPGA configuration bitstreams to hardware over PCIe. Inside altera_cvp_send_block(), the driver writes the payload as a sequence of 32-bit words for efficiency. After the aligned word loop, a trailing byte path handles the final 1-3 bytes when the buffer length is not a multiple of four.
The defective path casts the remaining buffer pointer to u32 * and dereferences it to obtain the final word. This read always accesses four bytes even when fewer bytes are valid. When the input buffer ends exactly at a page boundary or at the tail of a scatterlist segment, the extra bytes lie in unmapped or unrelated memory. The result is a kernel-mode out-of-bounds read that can fault the system.
Root Cause
The root cause is unsafe pointer arithmetic on a partial-tail buffer. The code assumes at least four bytes are always readable at the tail address without verifying the underlying mapping. The fix copies the remaining 1-3 bytes into a zero-initialized u32 on the stack before performing the final register write. Only the valid bytes are read from the source buffer, and any padding bits sent to hardware are zeros.
Attack Vector
Exploitation requires the ability to submit an FPGA image to the Altera CvP driver, typically through the kernel FPGA manager interface. A local actor with the privileges needed to load an FPGA image can craft a bitstream whose length is not word-aligned and whose buffer terminates at a page or scatterlist boundary. The impact is limited to a kernel read fault and denial of service rather than arbitrary code execution.
The fix is distributed across several stable kernel commits, including 2564ac3d3b8b, 3b8938f5fbcf, 447b3c893987, 4dc1051939e4, 827ec385458a, 8f3365ed2a5d, 9da70a43b5fe, and b138bc665e21. See the linked Linux kernel commits for the authoritative patch content.
Detection Methods for CVE-2026-89730
Indicators of Compromise
- Kernel oops or page fault messages referencing altera_cvp_send_block or the altera-cvp module in dmesg and /var/log/kern.log
- Unexpected FPGA reconfiguration failures reported through the FPGA manager sysfs interface
- Repeated attempts to load unusually sized bitstream images through /sys/class/fpga_manager/
Detection Strategies
- Audit kernel modules loaded on systems with Altera FPGAs and confirm whether altera-cvp is present with lsmod | grep altera_cvp
- Monitor for privileged processes invoking the FPGA manager write path with non-aligned image sizes
- Correlate kernel crashes with recent FPGA programming operations to identify triggering images
Monitoring Recommendations
- Forward kernel logs to a centralized logging platform and alert on faults referencing FPGA driver symbols
- Track file access to /dev/fpga* and /sys/class/fpga_manager/ device nodes for anomalous callers
- Baseline expected FPGA image sources and flag ad-hoc bitstream loads outside of provisioning workflows
How to Mitigate CVE-2026-89730
Immediate Actions Required
- Identify systems running the altera-cvp driver and inventory kernel versions in use
- Apply the stable kernel updates that incorporate the referenced commit hashes
- Restrict access to FPGA manager device nodes and sysfs entries to trusted administrative accounts
Patch Information
The fix has been merged across multiple Linux stable branches. Administrators should upgrade to a kernel release that includes one of the referenced commits, such as 2564ac3, 3b8938f, 447b3c8, 4dc1051, 827ec38, 8f3365e, 9da70a4, or b138bc6. Track distribution advisories for backported builds.
Workarounds
- Unload the altera-cvp module on systems that do not require Altera CvP FPGA programming using modprobe -r altera-cvp
- Blacklist the module in /etc/modprobe.d/ to prevent automatic loading until the patched kernel is deployed
- Enforce least-privilege on FPGA management tooling and remove unnecessary write access to FPGA device nodes
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
