GHSA-p75g-cxfj-7wrx Pebble has Arbitrary Local File Inclusion (LFI) Vulnerability via `include` macro

• Maven io.pebbletemplates:pebble: <= 3.2.3 (no fix yet)

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. • Jul 15, 2024 Maintainer Contacted to enable private vulnerability reporting • Jul 18, 2024 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. Jonathan is currently independent.