sqlparse: Reindentation of tuple lists causes near-cap quadratic CPU consumption

Summary

When SQL is formatted with reindentation enabled, ReindentFilter repeatedly rebuilds prefixes of the current statement to calculate token offsets. An attacker who controls SQL sent to this opt-in formatting path can supply a parenthesized tuple list that remains just below the grouping-token cap. Thousands of offset calculations then traverse an expanding token tree, causing multi-second CPU consumption from an input of roughly 16 KB and degrading service availability.

Details

ReindentFilter._get_offset() joins the tokens returned by _flatten_up_to_token() to calculate the current output position. Each call begins by flattening the current statement from its start and walks until the target token. Tuple-list reindentation invokes this calculation repeatedly as it processes many parenthesized values, so later calls redo an increasingly large amount of prior work.

The vulnerable path is reached through sqlparse.format(sql, reindent=True) and sqlformat --reindent. A carefully sized tuple list completes grouping below the configured token cap and then enters the expensive reindentation path; a slightly larger input may instead be rejected quickly by the cap.

Relevant code locations:

• sqlparse/formatter.py:170 — enabling ReindentFilter
• sqlparse/filters/reindent.py:30 — repeated flattening from the statement start
• sqlparse/filters/reindent.py:44 — prefix joining for offset calculation
• sqlparse/filters/reindent.py:216 — tuple-list processing path

PoC

A complete validated reproduction is attached as reindent_tuple_list_cpu_dos-poc.zip. The archive contains reproduction/ at its root, uses Git and Docker, and compares two same-shape tuple-list inputs formatted with reindentation enabled.

Extract the archive beside this report, then run:

./reproduction/run.sh

Observed result:

The 600-tuple baseline completed in 0.649 seconds, while the below-cap 1,425-tuple input completed in 4.999 seconds. The run emitted EVOHUNT_REINDENT_DOS_VERIFIED and completed successfully.

Verification method:

The verification helper formats two same-shape tuple-list payloads with reindent=True and fails unless the larger payload completes successfully, takes at least 2.0 seconds, and takes at least 4x the baseline.

Limitations:

No reproduction blocker was recorded. Timing varies by host, and exploitation requires the reindentation option or corresponding CLI mode to be enabled.

Impact

This is a CPU resource-exhaustion vulnerability in workflows that reindent attacker-controlled SQL. A small crafted tuple-list input can occupy a worker for several seconds, enabling request delays, reduced throughput, or worker starvation when payloads are processed repeatedly or concurrently.

The affected reindentation behavior is opt-in, and sqlparse itself does not provide network exposure; reachability depends on the consuming application or CLI workflow. The demonstrated effect is CPU consumption in a single formatting call, not process termination, code execution, or confidentiality or integrity impact.