CVE-2026-101302 in FreeBSD
Summary
by MITRE • 10/15/2026
TLS 1.3 embeds the actual record type as the last non-zero byte of the decrypted payload, optionally followed by zero padding. The code which searches for the inner record type had an off-by-one bug which could be triggered by an invalid frame, leading to an underflow followed by an unconditional NULL pointer dereference, causing a kernel panic.
A remote TLS 1.3 peer can send a specially crafted record to trigger a kernel panic, resulting in a Denial of Service (DoS).
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability described involves a critical implementation flaw within the TLS 1.3 protocol handling logic, specifically concerning the parsing and validation of decrypted payloads. In standard TLS 1.3 operations, after decryption, the system must identify the inner record type to proceed with further processing. This identification process relies on locating the actual record type byte, which is positioned as the last non-zero byte in the decrypted payload, potentially followed by zero padding bytes used for alignment or security purposes such as preventing timing attacks through constant-time comparisons. The core technical flaw stems from an off-by-one error in the code responsible for searching for this inner record type indicator. This logical defect allows a remote attacker to craft and send specially malformed TLS records that exploit the boundary condition miscalculation during the search algorithm execution.
When an invalid frame is processed, the flawed logic fails to correctly account for array bounds or pointer offsets relative to the decrypted data buffer. Specifically, the off-by-one error leads to an integer underflow when calculating memory addresses or indices used to access the record type field. This arithmetic mistake results in a NULL pointer dereference because the calculated address falls outside valid memory regions or points directly to null space rather than the intended payload location. In kernel-space implementations of TLS stacks, such as those found in Linux operating systems, this condition triggers an immediate and unhandled exception within the core system logic. The consequence is a deterministic kernel panic, which forces the affected system into an emergency halt state to prevent further corruption or security breaches that might arise from executing invalid memory operations.
From an operational impact perspective, this vulnerability constitutes a severe Denial of Service (DoS) vector against any service relying on TLS 1.3 connections handled by the vulnerable kernel implementation. A remote adversary does not require authentication or prior knowledge of internal system states to exploit this flaw; they merely need network connectivity and the ability to initiate TCP handshakes followed by sending crafted TLS records during the handshake or data transfer phases. The successful exploitation results in complete service unavailability for all users connected through that host, as the kernel crash typically requires a full reboot to restore functionality. This impacts availability integrity metrics significantly, disrupting business operations, breaking continuous services, and potentially causing cascading failures if load balancers or upstream dependencies rely on this node's uptime without adequate failover mechanisms.
This vulnerability aligns with CWE-190 Integer Overflow or Wraparound, as the root cause is an arithmetic error leading to invalid memory access, which subsequently manifests as CWE-476 NULL Pointer Dereference. In terms of adversarial tactics, it maps to MITRE ATT&CK technique T1499 Endpoint Denial of Service, where attackers aim to disrupt availability by exhausting resources or crashing systems rather than stealing data or gaining persistent access. Mitigation strategies primarily involve applying vendor-provided security patches that correct the boundary checks in the TLS parsing logic. Until patches are applied, network administrators should consider deploying intrusion prevention system rules to detect and block malformed TLS records exhibiting patterns consistent with this exploit vector, such as unusually short payloads or specific byte sequences indicative of crafted underflow attempts. Additionally, ensuring that kernel updates are promptly installed is critical for maintaining resilience against remote code execution precursors like this type of memory corruption flaw.