sqlparse: Quadratic O(n²) DoS in group_comments
Summary
A comment-only statement (-- c\n*n) may cause a Denial of Service (DoS).
Details
Location: sqlparse/engine/grouping.py:331-341 (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):
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:
group_commentsruns first ingroup()(grouping.py:439), before the_group_matchingtoken-count guard (grouping.py:34-39). So the entire quadratic cost is paid even on oversized input.MAX_GROUPING_TOKENSdoes not provide protection on this vector.- It sits on the primary sanitizer path:
format(sql, strip_comments=True), used by query loggers, SQL firewalls, ORMs, and migration tools.
PoC
Tested using Python 3.14:
import time, sqlparse
for n in (1000, 2000, 4000):
s = "-- c\n" * n
t = time.perf_counter()
sqlparse.format(s, strip_comments=True)
print(f"n={n:5d} format(strip_comments)={1000*(time.perf_counter()-t):7.1f} ms")Output:
n= 1000 format(strip_comments)= 106.0 ms
n= 2000 format(strip_comments)= 403.3 ms
n= 4000 format(strip_comments)= 1602.8 msTime increase of ~4× per 2× input (quadratic). parse() shows the identical curve. Instrumented scan counts are exactly 1.0M / 4.0M / 16.0M tokens for n=1000/2000/4000. A ~250 KB comment-only payload forces minutes of CPU regardless of the 10000 token cap.
Impact
Denial of Service
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | sqlparse | < 0.6.0 | 0.6.0 |
References
- https://github.com/andialbrecht/sqlparse/security/advisories/GHSA-f2ff-p2ww-7p4p
- https://github.com/andialbrecht/sqlparse/commit/ef2012a5eeb491e604dea2b00d516904a3830c87
- https://github.com/andialbrecht/sqlparse
- https://pypi.org/project/sqlparse
- https://github.com/advisories/GHSA-f2ff-p2ww-7p4p
- https://nvd.nist.gov/vuln/detail/CVE-2026-71491
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N- Weakness (CWE)
CWE-400, CWE-407- Platform
- Python (PyPI)
- Package
sqlparse- Disclosed
- 17.08.2026
- Updated
- 11.10.2026 15:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-3697 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-f2ff-p2ww-7p4p - CC BY 4.0
Vulnerability history: sqlparse
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 9
- First → latest
- 09.2021 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 5
- Medium 4
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 1
- 2024: 1
- 2025: 0
- 2026: 6
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sqlparse: Quadratic O(n²) DoS in group_comments this entry
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