CVE-2026-88832 in BusyBox
Summary
by MITRE • 09/23/2026
BusyBox romfs volume ID parsing uses unbounded strlen on attacker-controlled metadata, causing a heap buffer overflow when processing crafted filesystem images.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified in BusyBox involves a critical flaw within the read-only file system (romfs) volume identifier parsing logic. This issue stems from an improper handling of string lengths during the initialization and validation phases of romfs metadata processing. Specifically, the code relies on an unbounded call to the strlen function when analyzing attacker-controlled data embedded within crafted filesystem images. In standard C programming practices, relying on strlen without prior bounds checking or length verification is a dangerous pattern that assumes null-terminated strings are always present and correctly formatted. When this assumption fails due to maliciously constructed input, the application proceeds with incorrect memory calculations, leading directly to out-of-bounds access conditions.
From a technical perspective, the root cause lies in the failure to validate the integrity of the romfs superblock or volume header before attempting to parse string fields within it. The parser extracts metadata that includes identifiers which are expected to be null-terminated strings. However, if an attacker crafts a filesystem image where these fields lack proper termination characters or contain malformed data structures, the strlen function will continue reading memory beyond the intended buffer boundary until it encounters a zero byte somewhere in adjacent heap space. This behavior results in a significantly larger length value being computed than what was actually allocated for the target buffer. Consequently, subsequent operations that utilize this inflated length to copy or process data trigger a heap buffer overflow.
The operational impact of this vulnerability is severe, particularly given the widespread deployment of BusyBox in embedded systems, IoT devices, and bootloaders where romfs is commonly used as an initial ramdisk format. An attacker who can supply a maliciously crafted romfs image to a system running vulnerable versions of BusyBox can exploit this heap buffer overflow to achieve arbitrary code execution with the privileges of the process invoking the parser. This could allow for complete compromise of the device, including privilege escalation if the parsing occurs within a privileged context such as an initramfs script or bootloader stage. Furthermore, even without immediate code execution, the memory corruption can lead to denial-of-service conditions by crashing the application through segmentation faults or undefined behavior resulting from heap metadata corruption.
This vulnerability aligns with Common Weakness Enumeration (CWE) categories including CWE-120 Buffer Copy without Checking Size of Input and CWE-787 Out-of-bounds Write, as it involves writing data beyond allocated memory boundaries due to incorrect size calculations derived from untrusted input. In the context of the MITRE ATT&CK framework, this flaw facilitates initial access or privilege escalation techniques by allowing attackers to execute arbitrary code through crafted inputs that bypass standard validation checks. The exploitation vector typically requires physical access or network-accessible services that accept filesystem images for mounting or inspection, making it a significant risk in environments where external storage media is trusted without rigorous integrity verification.
Mitigation strategies must focus on enforcing strict input validation and implementing safe string handling practices within the BusyBox codebase. Developers should replace unbounded strlen calls with bounded alternatives such as strnlen when dealing with potentially malformed or attacker-controlled data, ensuring that length calculations never exceed predefined buffer limits. Additionally, robust error checking mechanisms should be implemented to validate romfs headers against expected structural constraints before any parsing operations commence. This includes verifying null-termination explicitly and rejecting images that do not conform to the specification. For system administrators and users, applying vendor-provided patches or updating BusyBox binaries is essential to remediate this risk. In environments where patching is delayed, restricting access to filesystem mounting capabilities and validating input sources can reduce the attack surface significantly.