CVE-2026-111134 in libfwsi
Summary
by MITRE • 10/15/2026
libfwsi through 20260522 contains a heap out-of-bounds read vulnerability in libfwsi_mtp_file_entry_values_read_data() that allows attackers to read past buffer bounds via crafted MTP file entry shell items. Attackers can embed a 10 to 73 byte shell item with item data size of 44 or more in .lnk files, jump lists or shell bags to crash libfwsi consumers.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in libfwsi versions up through 20260522 represents a critical heap-based out-of-bounds read condition located within the function libfwsi_mtp_file_entry_values_read_data(). This flaw arises from insufficient validation of data boundaries when processing Media Transfer Protocol file entry structures. Specifically, the library fails to adequately verify that the declared size of item data does not exceed the actual allocated buffer capacity or the remaining bytes available in the input stream. When a crafted MTP file entry is processed, the parsing logic attempts to read shell items with lengths ranging from ten to seventy-three bytes while simultaneously handling an item data size field set to forty-four bytes or more. This discrepancy between expected and actual memory access patterns leads to reads extending beyond the allocated heap region, exposing adjacent memory contents that were not intended for disclosure.
The operational impact of this vulnerability is significant because it allows attackers to achieve arbitrary information leakage from the process memory space where libfwsi is instantiated. By embedding maliciously crafted shell items within common Windows file system artifacts such as .lnk shortcut files, jump lists, or shell bags, an attacker can trigger the out-of-bounds read when a victim opens these files using software that relies on libfwsi for parsing MTP structures. The immediate consequence of this memory access violation is often application instability, manifesting as crashes in any consumer applications utilizing the library. However, beyond denial of service, the primary risk involves sensitive data exposure. Depending on what resides in adjacent heap memory at the time of exploitation, attackers may extract cryptographic keys, authentication tokens, or other private user information that was previously allocated and not yet overwritten by subsequent operations.
From a classification perspective, this vulnerability aligns with CWE-125, which defines out-of-bounds read errors where software reads past the end of an intended buffer. The attack vector leverages social engineering techniques to trick users into opening maliciously constructed files that appear legitimate but contain embedded payloads designed to exploit the parsing logic. In terms of tactical mapping under MITRE ATT&CK, this behavior corresponds to T1059 Command and Scripting Interpreter if used in conjunction with further exploitation steps, or more directly to T1083 File and Directory Discovery when the goal is merely enumerating system structures, though the core technical flaw falls squarely under data exfiltration techniques such as T1005 Data from Local System. The use of shell items within .lnk files also touches upon persistence mechanisms often seen in advanced persistent threats seeking to maintain access or gather intelligence about user activity through jump lists and shell bags.
Mitigation strategies for this vulnerability require immediate attention from both developers and end-users. Developers integrating libfwsi should ensure they are using a patched version released after the discovery of this flaw, as upstream fixes typically involve adding rigorous bounds checking before any memory read operations occur within the MTP file entry parsing routines. For organizations relying on affected software, it is advisable to implement strict input validation at the application layer if possible, although reliance solely on library patches remains the most effective defense. Additionally, security awareness training should emphasize caution when opening files from untrusted sources, particularly those containing shell extensions or metadata-rich structures like jump lists and shortcut files that are known vectors for triggering such parsing bugs. Endpoint detection systems can also be tuned to monitor for abnormal memory access patterns associated with heap corruption in processes handling file system metadata, providing an additional layer of defense against exploitation attempts targeting this specific class of vulnerabilities.