Handlebars syntax that renders content without HTML escaping. This is useful only in tightly controlled cases, because it allows raw markup to pass through the template layer. In security-sensitive applications, triple braces are a common source of XSS and should be heavily restricted.
Expanded Definition
Triple braces in Handlebars are an unescaped output mechanism, which means the template engine inserts the value as raw HTML instead of encoding special characters. That behaviour is deliberate, but it changes the trust boundary: the template no longer neutralises markup, so the safety of the page depends entirely on the data source and any sanitisation that happened earlier.
In secure application design, this is not a general-purpose formatting feature. It is a narrowly scoped escape hatch for content that has already been validated, sanitised, or generated from a trusted system. When developers use triple braces to “make formatting work”, they often bypass the very controls that prevent script injection, broken page structure, and unintended privilege of attacker-controlled content. Guidance in NIST SP 800-53 Rev 5 Security and Privacy Controls aligns with this principle by emphasising input validation, output protection, and secure configuration as layered controls rather than optional refinements.
Definitions vary across vendors on whether the risk should be described as a template engine issue, a secure coding issue, or an output encoding failure, but the operational concern is the same: once escaping is disabled, the burden shifts to upstream assurance. The most common misapplication is treating triple braces as harmless formatting syntax, which occurs when developers expose user-controlled fields directly to the template without sanitisation.
Examples and Use Cases
Implementing triple braces rigorously often introduces a content-governance constraint, requiring teams to balance presentation flexibility against the cost of sanitisation, review, and tighter publishing workflows.
- Rendering CMS-managed rich text where the HTML is produced by a trusted editor pipeline and checked before publication.
- Displaying controlled system-generated markup, such as status badges or server-side snippets, where the output is not influenced by end users.
- Embedding vetted content fragments in documentation portals, while keeping ordinary form fields on escaped output to reduce XSS exposure.
- Using template helpers to sanitise or whitelist tags before unescaped rendering, rather than passing raw user input straight through.
- Reviewing legacy Handlebars views to replace broad triple-brace usage with escaped output unless a specific risk acceptance and validation process exists.
Security teams often compare this pattern with controls discussed in OWASP Top 10, because the practical failure mode is usually a cross-site scripting condition created by unsafe output handling. The lesson is not that raw rendering is always forbidden, but that it should be explicitly justified, documented, and constrained to content that cannot be influenced by an attacker.
Why It Matters for Security Teams
Triple braces matter because they convert a template into a potential delivery path for active content. In application security reviews, that makes them a high-signal indicator of where escaping assumptions may have been broken. For security teams, the real issue is not the syntax itself but the control failure behind it: untrusted input, incomplete sanitisation, or inconsistent review of content paths that reach the browser.
This becomes especially important in systems that combine user-generated content, workflow automation, and agentic AI-assisted publishing. If an AI workflow can draft or transform content before it reaches a template, the question is no longer just “is the data trusted?” but also “has the transformation pipeline preserved safety guarantees?” That is why secure coding standards, change control, and content validation all intersect here. Organisations that treat triple braces as a simple developer convenience often discover that the template layer is the point where a latent injection issue becomes visible to users and exploitable by attackers.
Practitioners typically encounter the consequences after an XSS finding, a phishing-style content injection, or a compromised content workflow, at which point triple braces become operationally unavoidable to review and remove.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10 address the attack and risk surface, while NIST CSF 2.0, NIST SP 800-53 Rev 5, NIST AI RMF and NIST SP 800-63 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST CSF 2.0 | PR.AC-3 | Output handling affects who can introduce active content into a system. |
| NIST SP 800-53 Rev 5 | SI-10 | Input validation and output safety are central to preventing unsafe raw rendering. |
| OWASP Non-Human Identity Top 10 | Unescaped rendering can expose identity-linked automation and content workflows. | |
| NIST AI RMF | GOVERN | AI-assisted content generation can change trust assumptions before rendering. |
| NIST SP 800-63 | Identity assurance matters when content publishing rights control unescaped output. |
Bind publishing privileges to strong authentication and review the actors who can alter templates.
Related resources from NHI Mgmt Group
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Reviewed and updated by the NHIMG editorial team on August 24, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
