Medium [CVE-2026-56392] GNU coreutils unexpand: Denial of Service via crafted tab stop values

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 A flaw was found in GNU coreutils, specifically in the `unexpand` utility. This can lead to an undersized memory buffer, allowing subsequent operations to write beyond its boundaries.

Successful exploitation can cause the `unexpand` utility to crash, potentially resulting in a denial of service or enabling further memory manipulation. A local attacker could exploit this by providing crafted input, causing the utility to crash and potentially leading to a denial of service or arbitrary memory manipulation.

Red Hat severity: Moderate — CVSS 4.4 (CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L). Weakness: CWE-787.