Bug report
What happened?
This is an umbrella issue for 50 select bugs found using cpython-review-toolkit , distributed across ~350K lines of CPython C code (Modules/, Objects/, Python/).
Feel free to work on any report, opening an issue if one doesn't exist yet. Comment with the issue and respective gist/bug here and I'll update the table. If you find an issue listed below that is a duplicate of an existing report, let me know and I'll also mark it in the table.
Modules/ (18 gists)
Gist
Description
CPython Issue
gist _ssl.c: Py_DECREF(NULL) in SNI callback
#146080
gist _sqlite: collation assertion + missing PyErr_NoMemory
#146090
gist functools partial PyDict_Contains -1 as truthy
#146075 FIXED
gist _csv.c: _set_str missing NULL check
#146093 FIXED
gist _zoneinfo: SEGV in get_weak_cache
#146076 FIXED
gist _zoneinfo: missing PyErr_NoMemory in load_data
#146092 FIXED
gist termios: NULL to PyLong_AsLong
#146091 FIXED
gist _struct: segfault/assertion on uninitialized Struct
Fixed in 515ae40
gist pyexpat: ExternalEntityParserCreate crash
Fixed in e6b9a14
gist _interpqueuesmodule: use-after-free dangling last
#146427
gist selectmodule: errno < 0 always false
#146205 FIXED
gist _lsprof: exception clobbering
—
gist deque.copy() ref corruption on OOM
—
gist readline: begidx NULL on OOM
—
gist zlibmodule: PyErr_NewException unchecked
false alarm
gist socketmodule: audit hook ref/buffer leaks
#146245 FIXED
gist _interpchannelsmodule: missing PyErr_NoMemory
#150213
gist _interpretersmodule: SEGV on create under OOM
—
Objects/ (13 gists)
Gist
Description
CPython Issue
gist ExceptionGroup repr OOB — 3-line segfault
#146096 FIXED
gist SyntaxError.__init__ ref leaks on re-init#146250 FIXED
gist codeobject: code_richcompare swallows errors
#146199 FIXED
gist codeobject: co_tlbc NULL + replacement_locations leak
—
gist weakref WRAP_BINARY ref leak (~20 operators)
—
gist FrameLocalsProxy swallows/overwrites errors
—
gist typeobject: missing return -1 in type_ready
commit c398490
gist typeobject: buffer leak in slot_bf_getbuffer
#151346
gist object.c: PyObject_Print missing LeaveRecursiveCall
commit e2fa10e
gist structseq: get_type_attr_as_size NULL deref
#148119
gist genericaliasobject: two NULL dereference bugs
#148226 FIXED
gist odictobject: spurious PyErr_Clear
#151347
gist unicode_format: wrong return + PY_SSIZE_T_MIN UB
—
Python/ (16 gists)
Gist
Description
CPython Issue
gist import.c: wrong interpreter + double lock release
—
gist instrumentation.c: PyLong leak per monitoring call
—
gist instrumentation.c: use-after-Py_DECREF comparison
—
gist ceval.c: missing PyErr_NoMemory + PyEval_GetLocals NULL
—
gist bltinmodule: lazy_import NULL deref
—
gist crossinterp: UAF + leaked exception + shadowed var
—
gist compiler pipeline: 6 ref leaks and error bugs
#146442
gist marshal: 8 refs leaked on corrupt TYPE_CODE
#148418
gist pylifecycle: 5 init/fini cleanup bugs
—
gist initconfig: SET_ITEM macro leaks dict
#146244 FIXED
gist ast.c: LEAVE_RECURSIVE missing on 30 paths
—
gist hamt.c: sub_node leaked in bitmap ops
#150178
gist pythonrun: main_module ref leak
#146355 FIXED
gist modsupport: missing va_end (UB)
#146386 FIXED
gist legacy_tracing: unchecked PyLong_AsInt
—
gist optimizer_symbols: make_bottom NULL deref
#146388 FIXED
Duplicates (3 gists — same bugs uploaded from different runs)
Gist
Duplicate of
gist ExceptionGroup repr (dup of dceaa8b7)
gist sqlite collation (dup of 69aff7ff)
gist SSL SNI (dup of 50f98806)
These issues were found with Claude Opus 4.6, using the /cpython-review-toolkit:explore [file or directory] all deep command.
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
Output from running 'python -VV' on the command line:
Python 3.15.0a7+ (heads/main:e0f7c1097e1, Mar 17 2026, 18:10:52) [Clang 21.1.2 (2ubuntu6)]
Linked PRs
Reactions are currently unavailable
Bug report
What happened?
This is an umbrella issue for 50 select bugs found using cpython-review-toolkit, distributed across ~350K lines of CPython C code (Modules/, Objects/, Python/).
Feel free to work on any report, opening an issue if one doesn't exist yet. Comment with the issue and respective gist/bug here and I'll update the table. If you find an issue listed below that is a duplicate of an existing report, let me know and I'll also mark it in the table.
Modules/ (18 gists)
Objects/ (13 gists)
SyntaxError.__init__ref leaks on re-initPython/ (16 gists)
Duplicates (3 gists — same bugs uploaded from different runs)
These issues were found with Claude Opus 4.6, using the
/cpython-review-toolkit:explore [file or directory] all deepcommand.CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
Output from running 'python -VV' on the command line:
Python 3.15.0a7+ (heads/main:e0f7c1097e1, Mar 17 2026, 18:10:52) [Clang 21.1.2 (2ubuntu6)]
Linked PRs