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CVE-2026-71491 — sqlparse: Quadratic O(n²) DoS in group_comments

Affected: andialbrecht sqlparse

sqlparse is a non-validating SQL parser module for Python. Prior to 0.6.0, group_comments in sqlparse/engine/grouping.py repeatedly rescans comment-only statements before the MAX_GROUPING_TOKENS guard, causing quadratic CPU consumption through sqlparse.parse() and sqlparse.format(sql, strip_comments=True). This issue is fixed in version 0.6.0.

GHSA-f2ff-p2ww-7p4p — sqlparse: Quadratic O(n²) DoS in group_comments

Affected: PyPI: sqlparse

### Summary A comment-only statement (`-- c\n`*n) may cause a Denial of Service (DoS).

### Details Location: [sqlparse/engine/grouping.py:331-341](https://github.com/andialbrecht/sqlparse/blob/f80af6a4007f11ada847218df8c29dc859238290/sqlparse/engine/grouping.py#L332) (`group_comments`), invoked first in `group()` at `grouping.py:439`. Reachable via `sqlparse.parse()` and `sqlparse.format(sql, strip_comments=True)`.

A statement made of many single-line comments (`'-- c\n'` repeated) lexes in O(n) but `group_comments` is O(n²):

```python def group_comments(tlist): tidx, token = tlist.token_next_by(t=T.Comment) while token: eidx, end = tlist.token_not_matching( lambda tk: imt(tk, t=T.Comment) or tk.is_newline, idx=tidx) ... tidx, token = tlist.token_next_by(t=T.Comment, idx=tidx) ```

The `while` loop runs n times and each `token_next_by` / `token_not_matching` rescans the O(n) remaining tokens. When all tokens are comments/newlines nothing ever groups, yet the full scan is repeated per token.

Two following factors increase the severity:

1. `group_comments` runs first in `group()` (`grouping.py:439`), before the `_group_matching` token-count guard (`grouping.py:34-39`). So the entire quadratic cost is paid even on oversized input. `MAX_GROUPING_TOKENS` does not provide protection on this vector. 2. It sits on the primary sanitizer path: `format(sql, strip_comments=True)`, used by query loggers, SQL firewalls, ORMs, and migration…

PYSEC-2026-3697 — sqlparse: Quadratic O(n²) DoS in group_comments

Affected: PyPI: sqlparse

### Summary A comment-only statement (`-- c\n`*n) may cause a Denial of Service (DoS).

A statement made of many single-line comments (`'-- c\n'` repeated) lexes in O(n) but `group_comments` is O(n²):

Two following factors increase the severity: