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CPython 3.13-3.15 concurrency and memory-safety issue reports #157601
Description
Hello!
We are a team conducting Python security research. Recently, we investigated concurrency behavior in CPython and identified a set of reproducible correctness, concurrency, and memory-safety issues.
We evaluated free-threaded (FT) and conventional GIL-enabled builds separately. The confirmed findings cover CPython 3.13, 3.14, and 3.15. Across both build modes and releases, we identified 142 unique bugs in total.
Of these, 139 were confirmed in free-threaded builds and 34 were confirmed in conventional GIL-enabled builds. These two groups overlap: 31 bugs were confirmed in both build modes, while 3 were confirmed only in GIL-enabled builds.
The findings affect 29 library or extension components, 61 logical components, and 75 C source files. They primarily include Race Condition (CWE-362), TOCTOU Race Condition (CWE-367), Use After Free (CWE-416), and Improper Control of a Resource Through its Lifetime (CWE-664).
We have prepared a GitHub repository containing detailed bug reports, PoCs, and a comprehensive summary:
https://github.com/BaihongChen/cpython-concurrency-bugs
Complete component coverage
| Component | Category | 3.13 | 3.14 | 3.15 |
|---|---|---|---|---|
_remote_debugging |
Library/extension | — | — | ✓ |
array |
Library/extension | ✓ | ✓ | ✓ |
asyncio |
Library/extension | ✓ | — | — |
atexit |
Library/extension | ✓ | — | — |
collections |
Library/extension | ✓ | ✓ | ✓ |
compression.zstd |
Library/extension | — | ✓ | ✓ |
csv |
Library/extension | ✓ | — | — |
ctypes |
Library/extension | ✓ | ✓ | ✓ |
curses |
Library/extension | — | ✓ | — |
decimal |
Library/extension | ✓ | ✓ | — |
_suggestions / error suggestions |
Library/extension | ✓ | ✓ | — |
functools |
Library/extension | ✓ | ✓ | ✓ |
io |
Library/extension | ✓ | ✓ | — |
itertools |
Library/extension | ✓ | ✓ | ✓ |
json |
Library/extension | ✓ | ✓ | — |
locale |
Library/extension | — | ✓ | — |
| multibyte codecs | Library/extension | ✓ | ✓ | ✓ |
os |
Library/extension | ✓ | ✓ | ✓ |
pickle |
Library/extension | ✓ | ✓ | ✓ |
pyexpat |
Library/extension | ✓ | ✓ | ✓ |
re |
Library/extension | ✓ | ✓ | ✓ |
select |
Library/extension | ✓ | ✓ | ✓ |
sqlite3 |
Library/extension | ✓ | ✓ | ✓ |
ssl |
Library/extension | ✓ | ✓ | ✓ |
struct |
Library/extension | ✓ | ✓ | ✓ |
subprocess |
Library/extension | ✓ | ✓ | ✓ |
syslog |
Library/extension | ✓ | ✓ | ✓ |
termios |
Library/extension | ✓ | ✓ | ✓ |
tkinter |
Library/extension | ✓ | ✓ | ✓ |
xml.etree.ElementTree |
Library/extension | ✓ | ✓ | ✓ |
bytearray |
Built-in/core | ✓ | ✓ | ✓ |
bytes |
Built-in/core | ✓ | ✓ | ✓ |
| call protocol | Built-in/core | ✓ | ✓ | ✓ |
collections.OrderedDict |
Built-in/core | ✓ | ✓ | ✓ |
dict |
Built-in/core | ✓ | ✓ | ✓ |
| exceptions | Built-in/core | ✓ | ✓ | ✓ |
float |
Built-in/core | ✓ | ✓ | ✓ |
| frame | Built-in/core | ✓ | ✓ | ✓ |
| function | Built-in/core | ✓ | ✓ | ✓ |
| generator | Built-in/core | — | ✓ | — |
int |
Built-in/core | ✓ | ✓ | ✓ |
memoryview |
Built-in/core | ✓ | ✓ | ✓ |
| module | Built-in/core | ✓ | ✓ | ✓ |
| object protocol | Built-in/core | ✓ | ✓ | ✓ |
str |
Built-in/core | ✓ | ✓ | ✓ |
| struct sequence | Built-in/core | ✓ | ✓ | ✓ |
type |
Built-in/core | ✓ | ✓ | — |
ast |
Runtime/compiler | ✓ | ✓ | ✓ |
| C argument parsing | Runtime/compiler | ✓ | ✓ | ✓ |
| codec registry | Runtime/compiler | ✓ | ✓ | ✓ |
| compile/exec | Runtime/compiler | ✓ | ✓ | ✓ |
| compiler/evaluator | Runtime/compiler | ✓ | ✓ | ✓ |
contextvars |
Runtime/compiler | ✓ | ✓ | ✓ |
| cross-interpreter data | Runtime/compiler | ✓ | ✓ | ✓ |
| garbage collection | Runtime/compiler | ✓ | ✓ | ✓ |
| import machinery | Runtime/compiler | ✓ | ✓ | ✓ |
marshal |
Runtime/compiler | ✓ | ✓ | ✓ |
PyConfig |
Runtime/compiler | ✓ | ✓ | ✓ |
| runtime finalization | Runtime/compiler | ✓ | ✓ | ✓ |
sys |
Runtime/compiler | ✓ | ✓ | ✓ |
| traceback | Runtime/compiler | ✓ | ✓ | ✓ |
| warnings | Runtime/compiler | ✓ | — | — |
We hope these issues can be further confirmed and fixed in future releases. Thank you!
Activity
hugovk commentedon Sep 16, 2026
Dumping a mass report of 142 bugs isn't very helpful, and difficult for us to process. As you can se, we already have 6,921 open issues and 2,638 open PRs in our backlog.
Please can you check these really are "unique" and not duplicates of existing reports?
For example, I've not verified, but an LLM suggests the 8
memoryviewfor 3.14 reports all describe the same defect that gh-127716 (opened Dec 2024) tracks and will be fixed by #156248 (opened Aug 2026), currently under review.Also two of the
csvreports for 3.13 was already fixed in #141365 in Nov 2025 and backported to 3.14. The choice not to backport to 3.13 was likely deliberate, as free-threaded support is experimental in 3.13.It would be more helpful if you can pick a much smaller set (3-5?) of the most important reports, verify they're not duplicates, and evaluate whether they're worth fixing.
BaihongChen commentedon Sep 16, 2026
We further screened the findings and checked existing CPython issues. We selected the following five issues that meet the requested criteria. Each affects CPython 3.14 and 3.15, affects both free-threaded and GIL-enabled builds, and belongs to Built-in/core or Runtime/compiler:
compile(bytearray)source-storage UAFAn audit hook can release source storage that the compiler is still using, causing a deterministic heap-use-after-free.
int(bytearray)storage UAFA module import during large-integer conversion can invalidate the raw bytearray pointer, causing a heap-use-after-free.
PyImport_GetImporter()path-hook UAFThis Stable ABI function can continue using a freed
sys.path_hooksentry during the call.Module-finalization stderr reentry
A
sys.__stderr__callback can removesys.modulesentries that the finalization path still holds as borrowed references, causing a memory-safety failure.PyFunction_GetAnnotations()synchronization raceThe public C API lacks function-object synchronization. It can cause native failures in free-threaded builds and overwrite a completed annotations update in GIL-enabled builds. This differs from python/cpython#128714, which addressed the Python-level attribute getter rather than this public C API path.
We believe these five issues all have concrete PoCs, verifiable impact, and clear value in being fixed.