CVE-2026-93055 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
UDF symlink pathComponent header OOB read
udf_symlink_filler() can enter udf_pc_to_char() with a partial pathComponent header.
Validate that enough input remains for a complete pathComponent header before accessing it. Reject malformed symlink data that would otherwise make udf_pc_to_char() perform an out-of-bounds read.
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel's Universal Disk Format (UDF) filesystem driver contains a critical vulnerability related to the handling of symbolic links, specifically within the function responsible for filling buffer pages during symlink resolution. This issue arises when processing malformed or corrupted UDF media where pathComponent headers are incomplete or truncated. The core technical flaw lies in the udf_symlink_filler() routine, which is tasked with reading and interpreting metadata associated with symlinks stored on a UDF volume. Under normal circumstances, this function expects well-formed data structures that adhere to the UDF specification. However, when presented with disk images or physical media containing damaged filesystem structures, the driver fails to adequately validate the integrity of these headers before attempting to parse them.
The vulnerability manifests as an out-of-bounds read operation within the udf_pc_to_char() function. This internal helper is responsible for converting pathComponent data into character strings that can be used by the VFS layer. When udf_symlink_filler() passes a partial or truncated header to this converter, it does not verify whether sufficient input bytes remain in the buffer to satisfy the expected size of a complete pathComponent structure. Consequently, the function proceeds to read memory locations beyond the allocated bounds of the current data segment. This behavior constitutes an out-of-bounds read vulnerability, classified under CWE-125: Out-of-bounds Read in standard security taxonomies. The lack of boundary checks allows the kernel to access arbitrary memory regions adjacent to the intended buffer, potentially exposing sensitive kernel stack or heap contents depending on the allocation context and current system state.
From an operational perspective, this vulnerability poses significant risks regarding both confidentiality and stability. An out-of-bounds read can lead to information disclosure if the accessed memory contains cryptographic keys, authentication tokens, or other private data structures residing in adjacent memory pages. Furthermore, while reads are generally less severe than writes, they can still cause system instability by triggering kernel panics or oopses if the accessed address falls into unmapped or protected memory regions. In more complex scenarios involving subsequent processing of this corrupted data, the risk escalates to potential code execution vulnerabilities, although the primary impact here is limited to information leakage and denial of service through crashes. Attackers could exploit this by crafting malicious UDF images containing specially crafted symlink entries with truncated headers, thereby forcing the kernel into an unsafe memory access state upon mount or traversal operations.
This flaw aligns with ATT&CK technique T1083: File and Directory Discovery, as it involves improper handling of filesystem metadata that reveals internal system structures. It also reflects CWE-20: Improper Input Validation, highlighting a failure to enforce syntactic correctness on untrusted input derived from external storage media. The vulnerability underscores the importance of rigorous validation in kernel-level drivers that process data from potentially hostile or degraded sources such as removable drives or network-mounted filesystems.
To mitigate this risk, system administrators and developers must ensure that Linux kernels are updated with patches addressing this specific UDF symlink handling issue. For environments where UDF media is frequently used, implementing strict input validation at the driver level is essential to prevent malformed headers from reaching critical parsing functions. Additionally, deploying file integrity monitoring tools can help detect anomalies in filesystem structures before they trigger such vulnerabilities. Users should exercise caution when mounting untrusted or damaged UDF volumes and consider using sandboxed environments for initial inspection of suspicious media. Regular kernel updates remain the most effective defense against these types of low-level memory safety issues inherent to complex drivers like those found in the Linux VFS subsystem.