CVE-2020-11656: SQLite Use-After-Free Vulnerability

CVE-2020-11656 Overview

CVE-2020-11656 is a use-after-free vulnerability in SQLite versions through 3.31.1. The flaw resides in the ALTER TABLE implementation and is triggered by an ORDER BY clause that belongs to a compound SELECT statement. An attacker who can submit crafted SQL to a vulnerable SQLite instance can corrupt memory and potentially achieve remote code execution. The vulnerability affects the SQLite library directly and propagates to many downstream products that embed SQLite, including Oracle MySQL, NetApp ONTAP Select Deploy, Siemens SINEC, and Tenable.sc.

Critical Impact
Remote attackers can exploit this use-after-free condition over the network without authentication, leading to memory corruption, denial of service, or arbitrary code execution in any application embedding vulnerable SQLite versions.

Affected Products

SQLite through version 3.31.1
Oracle MySQL, MySQL Workbench, Outside In Technology, ZFS Storage Appliance Kit, Communications Network Charging and Control, Enterprise Manager Ops Center, Hyperion Infrastructure Technology, Communications Messaging Server
NetApp ONTAP Select Deploy Administration Utility, Siemens SINEC Infrastructure Network Services, Tenable.sc

Discovery Timeline

2020-04-09 - CVE-2020-11656 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-11656

Vulnerability Analysis

The vulnerability is a use-after-free condition [CWE-416] in SQLite's ALTER TABLE implementation. When SQLite processes a compound SELECT statement containing an ORDER BY clause during an ALTER TABLE operation, internal expression structures are freed but later dereferenced. This dangling pointer access corrupts the heap. Attackers can manipulate the freed memory region to control program flow within the embedding process. Because SQLite is linked directly into host applications, exploitation occurs within the address space and privilege context of those applications.

Root Cause

The defect stems from improper lifetime management of expression tree nodes during the rewriting performed by ALTER TABLE. The parser frees expression objects referenced by compound SELECTORDER BY clauses before all consumers release their references. Subsequent access to the freed object causes the use-after-free. The upstream fixes are tracked in SQLite check-ins d09f8c3621d5f7f8 and b64674919f673602.

Attack Vector

Exploitation requires the attacker to supply crafted SQL to a process that uses a vulnerable SQLite library. In networked deployments — such as MySQL servers, web applications that pass user-controlled SQL to embedded SQLite, or management utilities like NetApp ONTAP Select Deploy — the attack vector is the network. The triggering SQL combines an ALTER TABLE operation with a compound SELECT query whose ORDER BY clause references columns from the altered table. No authentication or user interaction is required on systems that expose SQL execution paths to untrusted input.

No verified public exploit code is available for this CVE. Refer to the SQLite source check-ins for the patch diff that illustrates the affected code paths.

Detection Methods for CVE-2020-11656

Indicators of Compromise

Unexpected crashes or segmentation faults in processes linking against libsqlite3 versions at or below 3.31.1.
Database access logs showing ALTER TABLE statements followed by compound SELECT queries with ORDER BY clauses from untrusted sources.
Heap corruption signatures or AddressSanitizer reports referencing SQLite expression handling routines.

Detection Strategies

Inventory all installed software and embedded libraries to identify SQLite versions ≤ 3.31.1 using software composition analysis tools.
Monitor SQL query logs in applications that accept user-supplied SQL for the combination of ALTER TABLE and compound SELECT with ORDER BY.
Apply vulnerability scanning against the products listed in vendor advisories from Oracle, NetApp, Siemens, and Tenable.

Monitoring Recommendations

Enable crash reporting and core dump collection on services that embed SQLite to capture exploitation attempts.
Forward database query telemetry to a centralized logging platform for anomaly analysis.
Correlate process crash events with preceding SQL workload patterns to identify exploitation attempts.

How to Mitigate CVE-2020-11656

Immediate Actions Required

Upgrade SQLite to version 3.32.0 or later on all systems where SQLite is directly installed.
Apply vendor patches from Oracle, NetApp, Siemens, FreeBSD, Gentoo, and Tenable for products that embed SQLite.
Restrict the ability for untrusted users to submit arbitrary SQL, particularly ALTER TABLE statements, to applications backed by SQLite.

Patch Information

The upstream fix is committed to the SQLite source tree under check-ins d09f8c3621d5f7f8 and b64674919f673602. Downstream fixes are published in the FreeBSD Security Advisory SA-20:22, Gentoo GLSA 202007-26, NetApp Advisory NTAP-20200416-0001, Oracle Critical Patch Updates (July 2020, October 2020, January 2021, April 2021), Siemens SSA-389290, and Tenable TNS-2021-14.

Workarounds

Disable or revoke privileges that allow untrusted principals to execute ALTER TABLE statements.
Place vulnerable services behind authenticated proxies or web application firewalls that filter SQL injection patterns.
Run SQLite-embedding services with reduced privileges and process-level sandboxing to limit the impact of memory corruption.

bash

# Verify installed SQLite version on Linux hosts
sqlite3 --version

# Identify processes loading libsqlite3 to scope remediation
lsof 2>/dev/null | grep -i libsqlite3

# Example: revoke ALTER privilege from untrusted MySQL accounts
mysql -u root -p -e "REVOKE ALTER ON *.* FROM 'untrusted_user'@'%'; FLUSH PRIVILEGES;"