CVE-2026-84243 is a vulnerability in the GNU C Library (glibc) affecting versions prior to 2.38-131.oe2403sp3. It involves the gettext family of functions improperly handling the LANGUAGE environment variable, allowing directory traversal and loading of message catalogs from arbitrary filesystem locations. This can lead to program crashes or potentially arbitrary code execution with the privileges of the affected program. The issue arises because the fix for a previous related vulnerability did not cover the LANGUAGE variable. Exploitation requires the attacker to control environment variables and place crafted files in readable locations, crossing trust boundaries without AT_SECURE restrictions.