CVE-2026-71491: sqlparse Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-f2ff-p2ww-7p4p",
  "modified" : "2026-08-17T17:21:00Z",
  "published" : "2026-08-17T17:21:00Z",
  "aliases" : [ "CVE-2026-71491" ],
  "summary" : "sqlparse: Quadratic O(n²) DoS in group_comments",
  "details" : "### Summary\nA comment-only statement (`-- c\\n`*n) may cause a Denial of Service (DoS).\n\n### Details\nLocation: [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)`.\n\nA statement made of many single-line comments (`'-- c\\n'` repeated) lexes in O(n) but `group_comments` is O(n²):\n\n```python\ndef group_comments(tlist):\n    tidx, token = tlist.token_next_by(t=T.Comment)\n    while token:\n        eidx, end = tlist.token_not_matching(\n            lambda tk: imt(tk, t=T.Comment) or tk.is_newline, idx=tidx)\n        ...\n        tidx, token = tlist.token_next_by(t=T.Comment, idx=tidx)\n```\n\nThe `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.\n\nTwo following factors increase the severity:\n\n1. `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.\n2. It sits on the primary sanitizer path: `format(sql, strip_comments=True)`, used by query loggers, SQL firewalls, ORMs, and migration tools.\n\n### PoC\nTested using Python 3.14:\n\n```python\nimport time, sqlparse\nfor n in (1000, 2000, 4000):\n    s = \"-- c\\n\" * n\n    t = time.perf_counter()\n    sqlparse.format(s, strip_comments=True)\n    print(f\"n={n:5d}  format(strip_comments)={1000*(time.perf_counter()-t):7.1f} ms\")\n```\n\nOutput:\n\n```\nn= 1000  format(strip_comments)=  106.0 ms\nn= 2000  format(strip_comments)=  403.3 ms\nn= 4000  format(strip_comments)= 1602.8 ms\n```\n\nTime 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.\n\n### Impact\nDenial of Service",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "sqlparse"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.6.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.5.5"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/andialbrecht/sqlparse/security/advisories/GHSA-f2ff-p2ww-7p4p"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/andialbrecht/sqlparse/commit/ef2012a5eeb491e604dea2b00d516904a3830c87"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/andialbrecht/sqlparse"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400", "CWE-407" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-17T17:21:00Z",
    "nvd_published_at" : null
  }
}