CVE-2026-84243 is a vulnerability in the GNU C Library (glibc) affecting versions prior to 2.34-189.oe2203sp4. It involves the gettext family of functions improperly handling the LANGUAGE environment variable, allowing an attacker to load message catalogs from arbitrary filesystem locations. Crafted message catalogs can cause crashes or enable arbitrary code execution with the privileges of the affected program. The flaw bypasses previous fixes that did not cover the LANGUAGE variable. Exploitation requires the attacker to control environment variables and place malicious files in readable locations, typically crossing a trust boundary without AT_SECURE protections.