CVE-2024-4340: sqlparse DOS Vulnerability via Recursion

CVE-2024-4340 Overview

CVE-2024-4340 is a Denial of Service vulnerability in the sqlparse Python library. Passing a heavily nested list to the sqlparse.parse() function leads to a RecursionError, causing the application to crash. This vulnerability allows remote attackers to disrupt services that rely on sqlparse for SQL parsing functionality by supplying maliciously crafted input.

Critical Impact

Applications using sqlparse to parse user-supplied SQL input are vulnerable to denial of service attacks through recursive stack exhaustion, potentially causing complete service disruption.

Affected Products

• sqlparse Python library (versions prior to the security fix)
• Applications and frameworks utilizing sqlparse for SQL parsing
• Debian-based systems with vulnerable sqlparse packages

Discovery Timeline

• 2024-04-30 - CVE CVE-2024-4340 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-4340

Vulnerability Analysis

This vulnerability is classified under CWE-674 (Uncontrolled Recursion), where the sqlparse library fails to properly limit recursion depth when processing nested data structures. The sqlparse.parse() function is designed to accept SQL statements for parsing and formatting. However, when presented with a heavily nested list structure, the parsing logic enters a recursive loop without adequate depth controls, eventually exhausting the Python interpreter's stack.

The attack can be executed remotely over a network without requiring any authentication or user interaction. An attacker simply needs to send a specially crafted nested list to any application endpoint that passes user input to the sqlparse.parse() function. The resulting RecursionError terminates the Python process or thread handling the request, leading to denial of service.

Root Cause

The root cause is insufficient input validation and missing recursion depth limits in the sqlparse parsing engine. When the parser encounters nested structures, it processes them recursively without checking the current recursion depth against a safe threshold. Python's default recursion limit (typically 1000) becomes a hard stop that manifests as a fatal RecursionError rather than a graceful handling of malicious input.

Attack Vector

The attack vector is network-based, requiring an attacker to send a crafted payload to an application that uses sqlparse. The attacker constructs a deeply nested list structure and submits it to any API endpoint or interface that processes SQL statements through sqlparse. Since no privileges or user interaction are required, the attack is straightforward to execute. The vulnerability affects availability by causing a complete denial of service condition, though confidentiality and integrity remain unaffected.

The exploitation mechanism involves creating a nested list with sufficient depth (typically exceeding Python's recursion limit). When this malformed input reaches the sqlparse.parse() function, the recursive descent parser attempts to process each nesting level, consuming stack frames until the interpreter raises a RecursionError exception. Without proper exception handling at the application level, this results in service termination.

Detection Methods for CVE-2024-4340

Indicators of Compromise

• Application crashes with Python RecursionError exceptions referencing sqlparse
• Repeated service restarts or process terminations in logs
• Incoming requests containing unusually nested data structures
• Error logs showing stack exhaustion or maximum recursion depth exceeded messages

Detection Strategies

• Monitor application logs for RecursionError exceptions originating from sqlparse modules
• Implement request payload inspection to detect deeply nested structures
• Set up alerting for abnormal service restart patterns that may indicate DoS attempts
• Review web application firewall logs for requests with excessive nesting depth

Monitoring Recommendations

• Configure application performance monitoring to track memory and stack usage patterns
• Enable detailed exception logging for the sqlparse library and dependent components
• Implement rate limiting on endpoints that process SQL input to slow down potential attacks
• Monitor Python interpreter process stability and restart frequency

How to Mitigate CVE-2024-4340

Immediate Actions Required

• Update sqlparse to the patched version containing the security fix
• Implement input validation to reject excessively nested data structures before parsing
• Add try-except blocks around sqlparse.parse() calls to gracefully handle RecursionError
• Consider implementing a recursion limit wrapper for sqlparse operations

Patch Information

The vulnerability has been addressed in a security patch. The fix is available in the GitHub commit b4a39d9850969b4e1d6940d32094ee0b42a2cf03. Debian users should apply updates as referenced in the Debian LTS Announcement. Additional technical details are available in the JFrog Vulnerability Report and the GitHub Security Advisory.

Workarounds

• Validate and sanitize all input before passing to sqlparse.parse() to prevent nested structures
• Implement application-level recursion limits using sys.setrecursionlimit() with appropriate exception handling
• Use process isolation or containerization to limit the blast radius of potential DoS conditions
• Deploy a web application firewall with rules to block requests containing deeply nested payloads

# Update sqlparse to the latest patched version
pip install --upgrade sqlparse

# Verify installed version
pip show sqlparse