Medium [CVE-2026-58012] buffer over-read in g_regex_replace via glib/gregex.c:string_append and g_utf8_next_char

A flaw was found in GLib. A buffer over-read can occur in the g_regex_replace function when used with the `G_REGEX_RAW` compile flag and case-change replacement escapes because the string_append function processes matched substrings using UTF-8 functions that assume valid UTF-8 input, even when the string is treated as raw bytes.

This vulnerability can cause a minor information disclosure of 1-5 bytes and a denial of service when the buffer over-read crosses a page boundary.

Any applications that use g_regex_replace() or g_regex_replace_eval() with the G_REGEX_RAW compile flag and allow user-controlled replacement strings containing case-change escapes (\u, \l, \U, \L) are vulnerable to this issue. Due to these reasons, this vulnerability has been rated with a moderate severity.

Red Hat severity: Moderate — CVSS 6.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L). Weakness: CWE-126.

Affected products named by the advisory: Red Hat Enterprise Linux 10.0 Extended Update Support; Red Hat Enterprise Linux 7 Extended Lifecycle Support; Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support; Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On; and 19 more.