CVE-2025-68799 Overview
CVE-2025-68799 is an integer underflow vulnerability in the Linux kernel's Communication CPU to Application CPU Interface (CAIF) subsystem. The flaw exists in the cffrml_receive() function, which extracts a length field from incoming packet headers. When Frame Check Sequence (FCS) is disabled, the function subtracts 2 from this length without first validating that the length value is at least 2. An attacker who sends a crafted packet containing a length field of 0 or 1 to an interface with FCS disabled triggers an integer underflow. The resulting condition can lead to memory exhaustion, kernel instability, and potential disclosure of uninitialized kernel memory.
Critical Impact
Remote attackers can trigger kernel memory exhaustion and potentially leak uninitialized kernel memory by sending malformed CAIF packets to interfaces with FCS disabled.
Affected Products
- Linux kernel (CAIF protocol stack)
- Multiple stable branches patched across seven upstream commits
- Systems with CAIF interfaces configured with FCS disabled
Discovery Timeline
- 2026-01-13 - CVE-2025-68799 published to the National Vulnerability Database
- 2026-04-15 - Last updated in NVD database
Technical Details for CVE-2025-68799
Vulnerability Analysis
The vulnerability resides in cffrml_receive(), a function within the CAIF Framing Layer responsible for processing incoming protocol frames. CAIF is used primarily for communication with modem hardware in Linux-based systems. The function reads a length field from the frame header and, depending on whether FCS protection is enabled, adjusts the expected payload length. With FCS disabled, the code subtracts 2 bytes (representing the absent checksum) from the parsed length value. The subtraction operates on an unsigned integer without bounds checking.
Root Cause
The root cause is missing input validation [CWE-191] before an arithmetic operation on attacker-controlled data. The function trusts the header-supplied length field and performs len -= 2 without confirming that len >= 2. When the attacker supplies a length of 0 or 1, the unsigned subtraction wraps around to a very large value. Downstream code then treats this wrapped value as a valid buffer length, leading to oversized memory operations or skb processing against an invalid length.
Attack Vector
Exploitation requires an attacker to deliver a malformed CAIF frame to a target interface configured with FCS disabled. The malicious frame contains a length field set to 0 or 1. Upon receipt, the kernel performs the underflowing subtraction and proceeds with operations that may exhaust kernel memory, destabilize the system, or expose uninitialized memory contents in subsequent processing. No verified public proof-of-concept code is available. See the upstream fix commits for technical patch details, including Kernel Git Commit 21fdcc0 and Kernel Git Commit f818cd4.
Detection Methods for CVE-2025-68799
Indicators of Compromise
- Unexpected kernel oops or memory allocation failures logged in dmesg from the caif subsystem
- Sudden kernel memory exhaustion on hosts exposing CAIF interfaces
- Receipt of CAIF frames with header length fields of 0 or 1 on interfaces with FCS disabled
Detection Strategies
- Audit kernel logs for warnings or stack traces referencing cffrml_receive or caif modules
- Inspect CAIF interface configurations to identify any with FCS disabled, which represent the exposed attack surface
- Monitor kernel slab allocator metrics for abnormal growth correlated with CAIF traffic
Monitoring Recommendations
- Forward kernel logs to a centralized logging platform and alert on caif-related errors
- Track running kernel versions across the fleet to identify hosts missing the upstream patches
- Baseline CAIF traffic volume and alert on anomalous spikes that could indicate exploitation attempts
How to Mitigate CVE-2025-68799
Immediate Actions Required
- Apply the upstream kernel patches that introduce the len >= 2 validation in cffrml_receive()
- Identify all systems with CAIF support compiled in and inventory interfaces operating with FCS disabled
- Restrict access to CAIF interfaces to trusted endpoints only until patches are deployed
Patch Information
The fix validates that len >= 2 before performing the subtraction in cffrml_receive(). Patches have been merged into multiple stable kernel branches. Reference the upstream commits: Kernel Git Commit 4ec2971, Kernel Git Commit 785c7be, Kernel Git Commit 8a11ff0, Kernel Git Commit c54091e, and Kernel Git Commit f407f1c. Consult your distribution vendor for backported kernel updates.
Workarounds
- Disable the caif kernel module on systems that do not require modem communication functionality
- Enable FCS on all active CAIF interfaces, which avoids the vulnerable subtraction code path
- Block untrusted sources from reaching CAIF endpoints via network segmentation or device-level access controls
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
