CVE-2025-68799: Linux Kernel CAIF Information Disclosure

CVE-2025-68799 Overview

A critical integer underflow vulnerability has been discovered in the Linux kernel's CAIF (Common Air Interface Framework) subsystem. The vulnerability exists in the cffrml_receive() function, which extracts a length field from packet headers and performs an arithmetic operation without proper input validation. When FCS (Frame Check Sequence) is disabled, the function subtracts 2 from the extracted length value without first verifying that the length is at least 2, leading to an integer underflow condition.

If an attacker sends a malicious packet with a length field of 0 or 1 to an interface with FCS disabled, the subtraction causes an integer underflow. This arithmetic error can result in memory exhaustion, kernel instability, and potential information disclosure if padding contains uninitialized kernel memory.

Critical Impact

Integer underflow in kernel CAIF subsystem can lead to memory exhaustion, kernel instability, and potential information disclosure through uninitialized kernel memory exposure.

Affected Products

• Linux Kernel (CAIF subsystem with FCS disabled)
• Systems using CAIF network interfaces
• Mobile and embedded devices utilizing CAIF protocol stack

Discovery Timeline

• 2026-01-13 - CVE CVE-2025-68799 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-68799

Vulnerability Analysis

The vulnerability resides within the cffrml_receive() function in the Linux kernel's CAIF framing layer. This function is responsible for processing incoming CAIF frames and extracting the payload length from packet headers. The core issue stems from a missing bounds check before performing arithmetic operations on untrusted input data.

When FCS validation is disabled on a CAIF interface, the function subtracts 2 bytes from the length field to account for framing overhead. However, the implementation fails to validate that the length value extracted from the packet header is greater than or equal to 2 before performing this subtraction. If an attacker crafts a packet with a length field of 0 or 1, the subtraction operation causes the unsigned integer to wrap around to an extremely large value due to integer underflow.

This malformed length value is then used in subsequent memory operations, potentially causing the kernel to attempt allocation of enormous memory buffers. The consequences include memory exhaustion as the system attempts to allocate oversized buffers, kernel panic or system instability due to failed allocations or corrupted memory state, and potential information disclosure if the system manages to allocate buffers and fills them with uninitialized kernel memory that may contain sensitive data.

Root Cause

The root cause is a missing input validation check in the cffrml_receive() function. The function extracts the length field from incoming packets and, when FCS is disabled, blindly subtracts 2 from this value without first verifying that the length is at least 2. This violates secure coding practices that require validation of all arithmetic operations on untrusted input to prevent integer overflow or underflow conditions.

Attack Vector

An attacker with the ability to send network traffic to a CAIF-enabled interface with FCS disabled can exploit this vulnerability. The attack requires crafting malicious CAIF packets with a length field set to 0 or 1 bytes. When these packets are processed by the vulnerable cffrml_receive() function, the integer underflow is triggered.

The attack is network-accessible on systems where CAIF interfaces are exposed and FCS is disabled. While exploitation does not require authentication, it does require the target system to have the specific vulnerable configuration (CAIF enabled with FCS disabled).

Detection Methods for CVE-2025-68799

Indicators of Compromise

• Unusual memory allocation failures or out-of-memory (OOM) conditions in kernel logs
• CAIF subsystem errors or crashes reported in dmesg output
• System instability or unexpected reboots on devices processing CAIF traffic
• Anomalous network traffic patterns with malformed CAIF frame headers

Detection Strategies

• Monitor kernel logs for CAIF-related error messages and memory allocation failures
• Implement network traffic analysis to detect CAIF frames with abnormal length fields (0 or 1 bytes)
• Deploy kernel-level monitoring to track memory allocation patterns associated with CAIF subsystem
• Use SentinelOne's kernel-level runtime protection to detect exploitation attempts

Monitoring Recommendations

• Enable verbose logging for the CAIF subsystem during security assessments
• Configure alerting for memory exhaustion events correlated with network activity
• Implement rate limiting on CAIF interfaces to mitigate potential DoS exploitation
• Monitor for kernel oops or panics related to the cffrml_receive() function

How to Mitigate CVE-2025-68799

Immediate Actions Required

• Apply the kernel patches from the provided stable kernel commits immediately
• If patching is not immediately possible, consider enabling FCS on CAIF interfaces as a temporary workaround
• Restrict network access to CAIF interfaces to trusted sources only
• Monitor systems for signs of exploitation attempts

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix adds proper validation to ensure that len >= 2 before performing the subtraction operation in cffrml_receive(). Multiple stable kernel commits have been released:

• Linux Kernel Commit 21fdcc0
• Linux Kernel Commit 4ec2971
• Linux Kernel Commit 785c7be
• Linux Kernel Commit 8a11ff0
• Linux Kernel Commit f818cd4

Organizations should update to kernel versions containing these patches as soon as possible.

Workarounds

• Enable FCS (Frame Check Sequence) on all CAIF interfaces to avoid triggering the vulnerable code path
• Disable CAIF interfaces entirely if not required for operational purposes
• Implement network-level filtering to drop malformed CAIF packets before they reach vulnerable systems
• Use firewall rules to restrict CAIF traffic to trusted network segments only

# Check if CAIF module is loaded
lsmod | grep caif

# If CAIF is not required, disable the module
sudo modprobe -r caif
echo "blacklist caif" | sudo tee /etc/modprobe.d/blacklist-caif.conf