CVE-2026-38755 in Busybox
Summary
by MITRE • 07/16/2026
A heap overflow in the evalcommand() function (shell/ash.c) of Busybox v1.38.0 allows attackers to cause a Denial of Service (DoS) via supplying a crafted input.
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Analysis
by VulDB Data Team • 07/16/2026
The vulnerability under discussion represents a critical heap buffer overflow condition within the evalcommand() function of Busybox version 1.38.0, specifically located in the shell/ash.c source file. This flaw manifests as a classic heap-based buffer overrun that occurs when the shell processes maliciously crafted input during command evaluation. The issue stems from inadequate bounds checking and memory management within the shell's command parsing mechanism, creating an exploitable condition that can be leveraged by remote attackers to disrupt system operations.
The technical implementation of this vulnerability involves the evalcommand() function failing to properly validate input lengths before attempting to allocate or copy data into heap-allocated buffers. When an attacker supplies malicious input containing excessive data or malformed sequences, the function processes this input without sufficient boundary checks, leading to memory corruption within the heap allocation space. This condition directly violates CWE-121, which categorizes heap-based buffer overflow vulnerabilities as a fundamental weakness in memory handling practices. The flaw operates at the intersection of shell command processing and memory management, making it particularly dangerous in embedded systems and networked environments where Busybox serves as a core system component.
The operational impact of this vulnerability extends beyond simple denial of service, as it creates potential pathways for more sophisticated attacks within constrained environments. While the immediate effect manifests as a DoS condition that can crash the shell process and potentially render system utilities unavailable, the underlying heap corruption could theoretically enable further exploitation techniques depending on the execution environment. The vulnerability affects systems running Busybox v1.38.0 across various platforms including embedded devices, routers, IoT appliances, and containerized environments where this lightweight shell implementation is commonly deployed. Attackers can exploit this issue through command-line input manipulation or by injecting malicious sequences into shell scripts that invoke the vulnerable function.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1059.004 for Unix Shell execution and represents a common vector for privilege escalation attempts in constrained environments where Busybox serves as the primary shell interface. The exploitation requires minimal privileges since it operates on the shell command processing layer, making it particularly dangerous in systems where users might have access to command-line interfaces or script execution capabilities. Mitigation strategies should focus on immediate patching of Busybox to version 1.38.1 or later, which contains the necessary memory boundary checks and input validation fixes. Additionally, system administrators should implement input sanitization at higher levels of the application stack, employ heap-based memory protection mechanisms like ASLR and DEP, and consider restricting shell access where possible to reduce attack surface exposure.
The broader implications of this vulnerability highlight the critical importance of robust memory management in embedded systems and lightweight utilities that serve as fundamental building blocks for larger software ecosystems. Given the widespread deployment of Busybox across networked devices, routers, and IoT platforms, this vulnerability demonstrates how seemingly minor flaws in core system components can create cascading security risks throughout entire device populations. Security teams should prioritize immediate remediation efforts and conduct comprehensive audits of all systems using affected Busybox versions to prevent exploitation attempts that could lead to more severe consequences including persistent backdoor installations or complete system compromise through chained vulnerabilities.