Medium [CVE-2026-6791] Denial of Service via stack exhaustion during tilde expansion

When expanding paths that begin with a tilde (~) followed by a username, the internal parse_tilde function extracts the username to determine the user's home directory. The implementation allocates memory for this username directly on the stack using the strndupa macro.

Because the size of this allocation was determined by the length of the user-supplied input without any bounds checks, passing an excessively long username e.g. thousands of characters, forces the thread to exhaust its stack space.

Thus if an application passes untrusted, attacker-controlled input to the wordexp function, an attacker can trigger a stack clash. A flaw was found in glibc.

When processing paths that start with a tilde (~) followed by a username, the `wordexp` function can be forced to allocate an excessive amount of memory on the program's stack. A remote attacker could exploit this by providing a very long username, leading to a stack exhaustion and causing a denial of service (DoS) for the affected application.

Red Hat severity: Moderate — CVSS 5.9 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-120.

Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9; Red Hat Hardened Images; Red Hat OpenShift Container Platform 4.