REDHAT-BUG-2494416: High severity GNU GDB vulnerability

A flaw was found in the GDB STABS debug format parser. The readmemberfunctions() function in gdb/stabsread.c processes C++ member function lists from STABS symbol data. When a class contains both destructor and non-destructor member functions, the code at lines 5086-5131 attempts to separate them into two lists. However, the linked list removal logic has a bug: the lastsublist tracking variable is updated to point to REMOVED destructor nodes instead of the previous retained node, and the continue path for non-destructor nodes does not update lastsublist at all. This causes destructor entries to remain in the sublist linked list while the length variable is decremented by hasdestructor. In the subsequent copy loop (lines 5163-5166), the allocated array has length elements but the loop iterates over all remaining sublist entries (more than length). The loop index i starts at length and decrements, going negative, causing writes before the allocated obstack array. The written data consists of struct fnfield members controlled by the attacker through crafted STABS strings. The obstack underflow can corrupt chunk metadata including function pointers, which are called on subsequent obstack operations, resulting in arbitrary code execution. The vulnerability triggers automatically when GDB expands partial symbol tables — any symbol-inspection command (break, ptype, info functions) on a binary containing crafted .stab/.stabstr sections is sufficient. The inferior process does not need to be executed.

Upstream: https://sourceware.org/git/binutils-gdb.git Affected: gdb/stabsread.c (readmemberfunctions, lines 5086-5166) Confirmed on: GDB 16.3-1, Debian trixie, x86-64, glibc 2.41 Reporter: JD Marsters (Bhut Red)