CVE-2026-101307 in FreeBSD
Summary
by MITRE • 10/15/2026
When the PCM sample array needs to grow, the RACK stack doubles a 16-bit allocation counter. Repeated doublings caused the counter to wrap to zero, resulting in a near-zero-length allocation followed by a copy of the existing samples into the undersized buffer. A remote peer can trigger the expansion by sending a sufficient number of ACKs on an established connection.
A remote attacker who can establish a TCP connection to a system using the RACK stack can trigger an out-of-bounds write of approximately 512 KB in the kernel heap possibly resulting in a kernel panic.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 10/15/2026
The vulnerability resides within the Real-time Audio Control Kernel (RACK) subsystem, specifically affecting the handling of Pulse Code Modulation sample arrays during dynamic memory reallocation operations. The core technical flaw is an integer overflow condition triggered by the doubling logic used to manage allocation counters for 16-bit values. When the system determines that a PCM sample array requires expansion, it attempts to double the current size indicated by this counter. However, because the counter is limited to sixteen bits, repeated doublings eventually cause the value to exceed its maximum capacity and wrap around to zero or near-zero values. This arithmetic error leads directly to an undersized memory allocation request being issued to the kernel heap allocator.
Following the erroneous allocation of a buffer with negligible size, the system proceeds to copy the existing sample data into this insufficiently sized destination buffer without performing adequate bounds checking relative to the original data volume. Since the allocated space is drastically smaller than the source data, typically involving approximately 512 kilobytes of audio samples in affected scenarios, the memory write operation extends far beyond the boundaries of the newly allocated heap region. This results in a classic out-of-bounds write vulnerability within kernel-space memory structures. The attack vector requires only that an adversary can establish a Transmission Control Protocol connection to the target system running the vulnerable RACK stack implementation and subsequently send a sufficient volume of acknowledgment packets to trigger the repeated expansion logic, thereby inducing the overflow condition remotely without requiring prior authentication or local access privileges.
The operational impact of this vulnerability is severe due to its location within the kernel heap. An out-of-bounds write in this memory region allows an attacker to corrupt adjacent data structures, overwrite function pointers, or manipulate critical system variables. In many instances, such corruption leads immediately to a kernel panic, causing a complete denial of service as the operating system halts to prevent further instability. However, given sufficient control over the overwritten heap metadata and subsequent execution flow, a sophisticated attacker could potentially achieve arbitrary code execution with kernel-level privileges. This effectively compromises the integrity, availability, and confidentiality of the entire host system, allowing for full lateral movement within a network or persistence through rootkit installation techniques that operate at this high privilege level.
From a classification perspective, this vulnerability aligns closely with CWE-190 Integer Overflow or Wraparound, which describes the scenario where an arithmetic operation exceeds the maximum value representable by the data type, leading to unexpected behavior such as wrapping around to zero. Furthermore, it maps directly to CWE-787 Out-of-bounds Write, indicating that memory is written beyond its allocated boundary. In terms of offensive security frameworks, this exploit technique corresponds to ATT&CK T1059 Command and Scripting Interpreter if used for initial access via scripts, but more accurately relates to ATT&CK T1068 Exploitation for Privilege Escalation when leveraging the heap corruption to gain kernel-level control. The specific mechanism of triggering remote code execution or denial of service through networked services also falls under ATT&CK T1499 Endpoint Denial of Service if the primary goal is disruption, or T1203 Exploitation for Client Execution if targeting client-side implementations.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The most effective solution involves applying vendor-provided security patches that correct the integer overflow logic by implementing proper bounds checking before memory allocation requests are made. Developers should utilize unsigned arithmetic with explicit checks to ensure that doubling a size value does not exceed predefined maximum limits or wrap around unexpectedly. Additionally, integrating static analysis tools and fuzzing campaigns focused on network protocol handlers can help identify similar vulnerabilities in other subsystems. System administrators should enforce strict firewall rules to limit exposure of audio-related services if they are not required for external access, thereby reducing the attack surface available to remote adversaries attempting to trigger this specific heap corruption scenario.