CVE-2026-56392 in coreutils
Summary
by MITRE • 07/24/2026
GNU coreutils unexpand is vulnerable to a heap-based buffer overflow due to an integer overflow during buffer allocation when processing large tab stop (-t) values. The multiplication used to calculate the allocation size can wrap around, resulting in an undersized buffer. When processing crafted input, subsequent writes exceed the allocated memory, leading to an out‑of‑bounds heap write.
When running GNU coreutils unexpand with attacker-provided large tab stop (-t) arguments, this behavior leads to a crash and potentially achieve a heap write primitive depending on memory layout.
This issue has been fixed in the commit b60a159fdc5bfcf9988d3a4cb6f53abe8ad5d35d
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Analysis
by VulDB Data Team • 07/24/2026
The vulnerability in GNU coreutils unexpand represents a critical heap-based buffer overflow that stems from an integer overflow during memory allocation processes. This flaw occurs specifically when the utility processes large tab stop values through the -t command-line argument, creating a scenario where mathematical operations used for buffer sizing produce incorrect results due to integer wraparound behavior. The underlying technical implementation fails to properly validate or sanitize input values before performing arithmetic operations that determine memory allocation sizes, leading to a fundamental miscalculation in heap memory management.
The operational impact of this vulnerability extends beyond simple crash conditions to potentially enable arbitrary code execution through heap manipulation primitives. When an attacker provides crafted input with excessively large tab stop values, the integer overflow causes the system to allocate insufficient memory buffers that subsequently become targets for out-of-bounds writes. This memory corruption pattern creates opportunities for attackers to manipulate heap metadata or overwrite critical program structures, effectively providing a foothold for more sophisticated exploitation techniques. The vulnerability directly aligns with CWE-190, which catalogs integer overflow conditions leading to buffer overflows and memory corruption issues.
The exploitation landscape for this vulnerability demonstrates how seemingly benign command-line utilities can become attack vectors when input validation fails at critical processing points. Attackers can leverage this flaw by carefully crafting tab stop values that trigger the integer overflow condition, causing the application to allocate memory that is significantly smaller than required for legitimate processing operations. The resulting heap write primitive allows for potential control flow hijacking through strategic memory corruption, making this a particularly dangerous vulnerability in environments where core system utilities are frequently executed with elevated privileges.
Security mitigations for this vulnerability involve implementing proper input validation and integer overflow detection mechanisms within the buffer allocation logic. The fix implemented in commit b60a159fdc5bfcf9988d3a4cb6f53abe8ad5d35d addresses the root cause by ensuring that arithmetic operations used to calculate memory requirements properly handle potential overflow conditions and validate input parameters before proceeding with allocation. Organizations should prioritize patching affected systems and implementing runtime protections such as address space layout randomization and stack canaries to reduce the exploitation surface. The vulnerability also highlights the importance of applying security patches promptly and maintaining up-to-date system configurations, as outlined in various cybersecurity frameworks including those referenced by the ATT&CK framework for defensive measures against common exploitation techniques targeting system utilities.
This particular vulnerability demonstrates how memory safety issues in widely-used open source utilities can create widespread security implications across multiple system environments. The combination of integer overflow and buffer overflows creates a perfect storm for exploitation opportunities, particularly in systems where core utilities are executed with elevated privileges or in automated processing contexts. The fix represents a fundamental correction to input validation procedures that should serve as a model for similar vulnerabilities in other system components, emphasizing the need for comprehensive security testing and code review processes that specifically target memory safety conditions.