vulnerability / NVI-00018576 / Revision 1
UltraJSON has a Memory Leak in ujson.dump() on Write Failure
GitHub lists this reviewed advisory for ujson. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
7.5 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
ujson
source listed<= 5.12.0
### Summary When `ujson.dump()` writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload. Code that uses `ujson.dumps()` rather than `ujson.dump()` or only JSON load/decode methods is unaffected. ### Details **Vulnerability Location:** - `src/ujson/python/objToJSON.c:913` - `objToJSONFile()` function start - `src/ujson/python/objToJSON.c:931` - Error return on write failure - `src/ujson/python/objToJSON.c:942` - Early return without cleanup **Root Cause:** The `objToJSONFile()` function allocates a Python string object via `ujson_dumps_internal()`, calls the file's `write()` method, and returns early if `write()` raises an exception—but never calls `Py_DECREF(string)` on the early exit path. ### PoC ```python import gc, tracemalloc, ujson class BadFile: def write(self, s): raise RuntimeError("boom") obj = {"x": "A" * 200000} def run(): try: ujson.dump(obj, BadFile()) except RuntimeError: pass run() tracemalloc.start() gc.collect() base = tracemalloc.get_traced_memory()[0] for
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
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04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-c38f-wx89-p2xg ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
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