CVE-2026-111133 in libfsapfs
Summary
by MITRE • 10/15/2026
libfsapfs through 20260921 contains an integer underflow in libfsapfs_key_encrypted_key_read_data() that allows attackers to trigger heap out-of-bounds reads via crafted KEK attributes. Attackers can supply a crafted encrypted APFS image with malformed HMAC or wrapped KEK attribute lengths to crash fsapfsinfo, pyfsapfs, dfVFS or plaso and read adjacent heap memory before password checks.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in libfsapfs versions up through 20260921 represents a critical security flaw rooted in improper validation of input data during the processing of Key Encrypted Key attributes within Apple File System images. Specifically, the function libfsapfs_key_encrypted_key_read_data fails to adequately check for integer underflow conditions when calculating buffer sizes or offsets based on attribute lengths provided by an attacker-controlled encrypted APFS image. This logical error allows malicious actors to manipulate internal variables such that arithmetic operations result in negative values or unexpectedly small positive values, which are then used as bounds for memory allocation or access routines. The core technical flaw lies in the lack of rigorous boundary checks before these calculated values influence heap-based data structures, creating a scenario where subsequent read operations exceed the allocated buffer limits.
This integer underflow directly facilitates heap out-of-bounds reads, enabling an attacker to leak sensitive information from adjacent regions of memory that should remain inaccessible. By supplying crafted encrypted APFS images with malformed HMACs or incorrectly specified wrapped KEK attribute lengths, adversaries can trigger this vulnerability before any password verification takes place. This pre-authentication execution context is particularly dangerous because it allows exploitation without requiring valid credentials for the target file system. The ability to read arbitrary heap memory prior to authentication significantly lowers the barrier for attack and increases the potential impact of successful exploitation by exposing cryptographic keys, session tokens, or other sensitive data stored in nearby memory locations.
The operational impact of this vulnerability extends across multiple tools that rely on libfsapfs for parsing APFS structures, including fsapfsinfo, pyfsapfs, dfVFS, and plaso. These applications are commonly used by digital forensics professionals and incident responders to analyze disk images. An attacker who can distribute a maliciously crafted APFS image could cause these tools to crash due to segmentation faults or memory access violations, resulting in denial of service for forensic workflows. More critically, the ability to read adjacent heap memory poses a severe confidentiality risk, potentially leading to information disclosure that compromises the integrity of investigations or exposes sensitive data from other processes sharing the same address space if executed within certain environments.
From a classification perspective, this vulnerability aligns with CWE-190 Integer Overflow or Wraparound and CWE-787 Out-of-bounds Read, as it involves incorrect arithmetic leading to unsafe memory access. In terms of attack vectors, it corresponds to ATT&CK technique T1552 Unsecured Credentials, specifically the sub-technique for accessing credential material from local system images, although in this case, the immediate impact is information disclosure rather than direct credential theft. The exploitation path also reflects aspects of T1078 Valid Accounts if viewed through the lens of bypassing authentication checks via pre-authentication flaws, though it primarily serves as a precursor to more severe attacks such as remote code execution or privilege escalation depending on how the leaked data is utilized by subsequent stages of an attack chain.
Mitigation strategies must focus on immediate patching and defensive coding practices within libfsapfs and its dependent tools. Developers should implement strict validation checks for all integer calculations involving buffer sizes, ensuring that inputs are validated against maximum allowable limits before being used in arithmetic operations. Specifically, the function handling KEK attributes must verify that attribute lengths do not result in underflows or exceed allocated memory boundaries. For users of fsapfsinfo, pyfsapfs, dfVFS, and plaso, it is imperative to update to patched versions as soon as they become available. In environments where immediate patching is not feasible, deploying input sanitization layers at the application boundary can help filter out malformed attributes before they reach the vulnerable library functions. Additionally, enabling memory protection mechanisms such as Address Space Layout Randomization and heap hardening features in operating systems can reduce the likelihood of successful exploitation by making it more difficult for attackers to predict or control adjacent memory contents.