CVE-2026-88839 in BusyBox
Summary
by MITRE • 09/23/2026
BusyBox passwd/group tokenize() references a stale endpoint pointer after trimming, causing an out-of-bounds write of heap pointers.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified in BusyBox involves a critical memory management flaw within the tokenization logic used by the passwd and group utilities. Specifically, the issue resides in the handling of string endpoints during the parsing process where a pointer is not properly updated or validated after trimming operations are performed on input data. This oversight leads to a scenario where the application attempts to write heap pointers using an endpoint reference that no longer points to valid memory within the expected bounds. The root cause is classified under CWE-787, which denotes out-of-bounds write vulnerabilities, indicating that the software writes data beyond the intended boundary of a buffer or allocated memory region.
From a technical perspective, this flaw arises because the pointer arithmetic used to track string boundaries fails to account for changes in length resulting from trimming operations such as whitespace removal or character stripping. When the endpoint is trimmed but not re-evaluated against the current state of the heap allocation, subsequent write operations may target memory locations that are either unmapped or belong to other objects within the heap structure. This can result in corruption of adjacent metadata structures, such as chunk headers used by the allocator for managing free and allocated blocks. The exploitation potential is significant because an attacker who can influence the input data passed to these utilities might trigger this out-of-bounds write, potentially leading to arbitrary code execution or denial of service conditions depending on how the corrupted memory is subsequently accessed.
The operational impact of this vulnerability extends beyond simple application crashes. In embedded systems and IoT devices that rely heavily on BusyBox for basic system administration tasks, compromising the passwd or group utilities can allow an attacker to escalate privileges by modifying authentication credentials or user groups without proper authorization checks if the heap corruption allows bypassing security boundaries. Furthermore, since these tools are often executed with elevated privileges during system setup or maintenance, successful exploitation could provide a foothold for deeper network intrusion. The vulnerability aligns with ATT&CK technique T1059, Command and Scripting Interpreter, as it involves manipulating inputs to execute unintended actions through the abuse of local utilities that handle sensitive configuration data.
Mitigation strategies must focus on rigorous input validation and safe pointer management practices within the source code. Developers should ensure that all string manipulation functions update endpoint pointers correctly after any modification such as trimming or truncation. Implementing bounds checking before every write operation to heap memory is essential to prevent out-of-bounds writes. Additionally, enabling compiler-based security features like stack canaries and Address Sanitizer during development phases can help detect these issues early in the lifecycle. For end-users, applying vendor-provided patches that address this specific tokenization logic flaw is critical to maintaining system integrity. Regular auditing of third-party components used in embedded environments remains a best practice to identify such low-level memory safety violations before they are deployed in production systems.