CVE Vulnerabilities


Improper Restriction of XML External Entity Reference

Published: Feb 22, 2024 | Modified: Feb 22, 2024
CVSS 3.x
CVSS 2.x

The CodeQL CLI repo holds binaries for the CodeQL command line interface (CLI). Prior to version 2.16.3, an XML parser used by the CodeQL CLI to read various auxiliary files is vulnerable to an XML External Entity attack. If a vulnerable version of the CLI is used to process either a maliciously modified CodeQL database, or a specially prepared set of QL query sources, the CLI can be made to make an outgoing HTTP request to an URL that contains material read from a local file chosen by the attacker. This may result in a loss of privacy of exfiltration of secrets. Security researchers and QL authors who receive databases or QL source files from untrusted sources may be impacted. A single untrusted .ql or .qll file cannot be affected, but a zip archive or tarball containing QL sources may unpack auxiliary files that will trigger an attack when CodeQL sees them in the file system. Those using CodeQL for routine analysis of source trees with a preselected set of trusted queries are not affected. In particular, extracting XML files from a source tree into the CodeQL database does not make one vulnerable. The problem is fixed in release 2.16.3 of the CodeQL CLI. Other than upgrading, workarounds include not accepting CodeQL databases or queries from untrusted sources, or only processing such material on a machine without an Internet connection. Customers who use older releases of CodeQL for security scanning in an automated CI system and cannot upgrade for compliance reasons can continue using that version. That use case is safe. If such customers have a private query pack and use the codeql pack create command to precompile them before using them in the CI system, they should be using the production CodeQL release to run codeql pack create. That command is safe as long as the QL source it precompiled is trusted. All other development of the query pack should use an upgraded CLI.


The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.

Extended Description

XML documents optionally contain a Document Type Definition (DTD), which, among other features, enables the definition of XML entities. It is possible to define an entity by providing a substitution string in the form of a URI. The XML parser can access the contents of this URI and embed these contents back into the XML document for further processing. By submitting an XML file that defines an external entity with a file:// URI, an attacker can cause the processing application to read the contents of a local file. For example, a URI such as “file:///c:/winnt/win.ini” designates (in Windows) the file C:\Winnt\win.ini, or file:///etc/passwd designates the password file in Unix-based systems. Using URIs with other schemes such as http://, the attacker can force the application to make outgoing requests to servers that the attacker cannot reach directly, which can be used to bypass firewall restrictions or hide the source of attacks such as port scanning. Once the content of the URI is read, it is fed back into the application that is processing the XML. This application may echo back the data (e.g. in an error message), thereby exposing the file contents.

Potential Mitigations