CVE-2026-58012

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. This flaw can cause a buffer over-read of 1-5 bytes, leading to a minor information disclosure and a denial of service when the buffer over-read crosses a page boundary. Due to these reasons, this vulnerability has been rated with a moderate severity.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this vulnerability, implement strict input validation to sanitize user-supplied replacement strings, specifically rejecting or escaping case-change modifiers (\u, \l, \U, \L) before calling g_regex_replace() or g_regex_replace_eval() when the G_REGEX_RAW compile flag is used. Removing the G_REGEX_RAW flag or hardcoding the replacement strings will completely neutralize this issue.