CVE-2026-55760: Handlebars.java Path Traversal Arbitrary File Read Vulnerability

Technical summary

CVE-2026-55760 is a path traversal vulnerability (CWE-22) in Handlebars.java versions prior to 4.5.2. The flaw occurs in the FileTemplateLoader and ClassPathTemplateLoader implementations when user-controlled input is passed directly to Handlebars.compile(). These loaders construct file paths from template names without adequate canonicalization or validation, enabling directory traversal attacks. An attacker can craft a template name containing path traversal sequences to access files outside the designated template directory. The vulnerability has a CVSS 3.1 score of 7.5 (High) with CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N, indicating network-accessible exploitation with high confidentiality impact but no authentication requirement.

Business impact

Organizations using vulnerable Handlebars.java versions face confidentiality breaches. An attacker can read sensitive files such as configuration files, private keys, environment files, application source code, or other data stored on the same filesystem as the application. This could lead to credential theft, intellectual property loss, or discovery of secondary vulnerabilities. The impact severity is amplified in cloud-hosted or multi-tenant environments where sensitive data may be colocated. There is no integrity or availability impact, but the unauthorized information disclosure could enable subsequent attacks or regulatory compliance violations.

Affected systems

Any application using Handlebars.java (also known as Handlebars for Java) versions before 4.5.2 is vulnerable if it allows user-controlled input to influence template selection. This is particularly common in web applications that use dynamic template rendering based on URL paths, request parameters, or database values. Applications using FileTemplateLoader or ClassPathTemplateLoader are at greatest risk. Organizations should audit their dependency management systems, build artifacts, and running instances to identify Handlebars.java usage and version.

Exploitability

This vulnerability has a low barrier to exploitation. No authentication, special privileges, or user interaction is required. An attacker simply needs to craft a malicious request with path traversal sequences in the template name parameter and send it to the vulnerable application over the network. The attack is straightforward enough that automated scanning tools and opportunistic threat actors will likely identify and attempt exploitation quickly. The fact that this is not yet in the CISA KEV catalog does not diminish the risk; organizations should assume active exploitation is possible or imminent.

Remediation

Upgrade Handlebars.java to version 4.5.2 or later. Verify the patch version in your build dependencies (Maven pom.xml, Gradle build.gradle, etc.) and in running environments. For environments where immediate upgrading is not feasible, implement input validation to ensure template names do not contain path traversal sequences such as `../`, `..\`, or absolute paths. Use allowlisting of permitted template names where possible. Additionally, restrict filesystem permissions on the application process to limit the scope of readable files.

Patch guidance

Update Handlebars.java to 4.5.2 or a later stable release through your package management system (Maven Central, Gradle, etc.). If using Maven, update the dependency version in pom.xml and run `mvn clean dependency:resolve` to verify resolution. For Gradle, update the version in build.gradle and run `gradle build`. After patching, restart the application and verify that template loading still functions correctly. Test with your actual template directory structure to ensure no regression. If you have custom template loaders, review them for similar path traversal risks.

Detection guidance

Monitor application logs for template loading errors or unusual template name requests containing path traversal sequences (e.g., requests with `../` or `..\`). Configure Web Application Firewalls (WAF) or reverse proxies to block requests with encoded or raw path traversal patterns in parameters typically used for template selection. Conduct a code review of your application to identify where user input flows into Handlebars.compile() calls. Use static analysis tools (SAST) configured to detect CWE-22 patterns. In network monitoring, watch for repeated requests attempting different path traversal payloads, which may indicate active scanning or exploitation attempts.

Why prioritize this

This vulnerability merits prompt prioritization due to its high CVSS score (7.5), ease of exploitation (no authentication required), and direct path to sensitive data exposure. Path traversal vulnerabilities are among the most frequently exploited issues in web applications. The combination of network accessibility, low complexity, and confidentiality impact makes this a credible near-term risk. Organizations should prioritize patching within days rather than weeks, especially for internet-facing or customer-facing applications.

Risk score, explained

The CVSS 3.1 score of 7.5 reflects the following factors: Network-based attack vector (AV:N) with no special network access required; low attack complexity (AC:L) meaning no special conditions are needed to exploit it; no privileges or user interaction required (PR:N, UI:N); unchanged security scope (S:U); and high confidentiality impact (C:H) due to arbitrary file read capability. The lack of integrity or availability impact prevents a critical score, but the ease of exploitation and direct confidentiality breach justify a High severity rating.

Frequently asked questions