CVE-2026-77658: Dia: dia: stack buffer overflow in bus object via unvalidated handle count in project files
A flaw was found in Dia's Network Bus object loader. When opening a crafted Dia project (.dia) file, the bushandles attribute supplies numhandles without validation. Later, when a bus handle is moved, bushandlemoved() allocates two arrays on the stack using galloca() sized by numhandles, which can exhaust the thread stack and cause memory corruption, application crash, or potentially arbitrary code execution. The same galloca pattern exists in objects/Misc/tree.c.
Other sources
A stack-based buffer overflow vulnerability exists in the Dia diagram editor when processing Network Bus objects from Dia XML project files.
In objects/network/bus.c, busload() reads the number of bus handles from the file attribute "bushandles" using attributenumdata() without validating an upper bound:
bus->numhandles = attributenumdata(attr);
When a bus handle is subsequently moved, bushandlemoved() allocates two temporary arrays on the stack:
parallel = (real )galloca(numhandles sizeof(real)); perp = (real )galloca(numhandles sizeof(real));
Because numhandles is fully attacker-controlled via the project file, sufficiently large values (for example 262144 or higher) cause galloca() to consume more stack space than the default thread stack limit (typically 8 MB on Linux), resulting in stack overflow, SIGSEGV, and potential stack frame / return-address corruption.
An attacker can embed a Bus object with an excessive bushandles count in a malicious .dia file. Exploitation requires the victim to open the file in Dia (file dialog, command line, or file association) and trigger handle manipulation (moving a bus handle), which exercises the vulnerable code path.
The identical galloca pattern is present in objects/Misc/tree.c (copied from bus.c) and is likely vulnerable to the same class of attack via Tree objects.
Affected versions: Dia 0.98.0 and earlier versions containing this code; issue confirmed on upstream master as of 2026-08-21. Upstream report: https://gitlab.gnome.org/GNOME/dia/-/issues/581
— MITRE