GHSA-p75g-cxfj-7wrx

### Summary

If untrusted user input is used to dynamically create a `PebbleTemplate` with the method `PebbleEngine#getLiteralTemplate`, then an attacker can include arbitrary local files from the file system into the generated template, leaking potentially sensitive information into the output of `PebbleTemplate#evaluate`. This is done via the `include` macro.

### Details

The `include` macro calls `PebbleTempateImpl#resolveRelativePath` with the `relativePath` argument passed within the template:

Example template: ``` {% include [relativePath] %} ``` When `resolveRelativePath` is called, the `relativePath` is resolved against the `PebbleTemplateImpl.name` variable.

```java /** * This method resolves the given relative path based on this template file path. * * @param relativePath the path which should be resolved. * @return the resolved path. */ public String resolveRelativePath(String relativePath) { String resolved = this.engine.getLoader().resolveRelativePath(relativePath, this.name); if (resolved == null) { return relativePath; } else { return resolved; } } ``` https://github.com/PebbleTemplates/pebble/blob/82ad7fcf9e9eaa45ee82ae3335a1409d19c10263/pebble/src/main/java/io/pebbletemplates/pebble/template/PebbleTemplateImpl.java#L380

Unfortunately, when the template is created from a string, as is the case when `PebbleEngine#getLiteralTemplate` is used, the `PebbleTemplateImpl.name` variable is actually the entirety of the contents of the template, not a filename as the logic expects. The net result is that the `relativePath` is resolved against the system root directory. As a result, files accessible from the root directory of the filesystem can be included into a template.

### PoC

The following test demonstrates the vulnerability:

```java PebbleEngine e = new PebbleEngine.Builder().build();

String templateString = """ {% include '/etc/passwd' %} """; PebbleTemplate template = e.getLiteralTemplate(templateString);

try (final Writer writer = new StringWriter()) { template.evaluate(writer, new HashMap<>()); System.out.println(writer); } ```

As an attacker, the following malicious template demonstrates the vulnerability:

``` {% include '/etc/passwd' %} ```

### Impact

This is an arbitrary Local File Inclusion (LFI) vulnerability. It can allow attackers to exfiltrate the contents of the local filesystem, including sensitive files into `PebbleTemplate` output. This can also be used to access the `/proc` filesystem which can give an attacker access to environment variables.

### Fix

There exists no published fix for this vulnerability. The best way to mitigate this vulnerability is to disable the `include` macro in Pebble Templates.

The following can safeguard your application from this vulnerability:

```java new PebbleEngine.Builder() .registerExtensionCustomizer(new DisallowExtensionCustomizerBuilder() .disallowedTokenParserTags(List.of("include")) .build()) .build(); ```

### Report Timeline

Vulnerability was reported under the Open Source Security Foundation (OpenSSF) [Model Outbound Vulnerability Disclosure Policy: Version 0.1](https://openssf.org/about/vulnerability-disclosure-policy/).

- [Jul 15, 2024](https://github.com/PebbleTemplates/pebble/issues/680#issue-2409727829) Maintainer Contacted to enable private vulnerability reporting - [Jul 18, 2024](https://github.com/PebbleTemplates/pebble/issues/680#issuecomment-2236970984) I opened a GHSA to report this vulnerability to the maintainer https://github.com/PebbleTemplates/pebble/security/advisories/GHSA-7c6h-hmf9-7wj7 (private link) - Jul 29, 2024 GHSA updated to ping maintainer about vulnerability, no response - Oct 1, 2024 GHSA updated to ping maintainer about vulnerability, no response - Nov 15, 2024 GHSA updated to inform maintainer that disclosure timeline had lapsed, no response. - Feb 19, 2025 GHSA updated to inform maintainer that disclosure would occur imminently, no response. - Feb 24, 2025 this GHSA was created to disclose this vulnerability **without a patch available**.

For further discussion, see this issue: https://github.com/PebbleTemplates/pebble/issues/688

### Credit

This vulnerability was discovered by @JLLeitschuh while at [Chainguard Labs](https://www.chainguard.dev). Jonathan is currently independent.