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The short answer
Evaluate generated output at the application component that consumes it. Text safe to display as plain prose may be unsafe when interpreted as HTML, a command, a query, or a file path. Define the intended representation, validate the consumer boundary, and test harmless payloads that reveal unintended interpretation.
What to take away
- Identify the actual downstream interpreter.
- Prefer constrained representations over executable text.
- Test the rendered or executed result, not only the model response.
Sources checked . Research synthesis and Rubrex recommendations. Examples and local experiments are labeled; they are not client results.
Map output to its consumer
OWASP’s improper-output-handling guidance concerns downstream use of LLM output. Rubrex recommends listing each consumer separately: plain-text view, rich-text renderer, search query, database adapter, shell wrapper, or file writer. One sanitizer should not be assumed appropriate for every context.
Use a synthetic report builder that renders model-produced titles and links in a web view. The accepted behavior is a readable title and a link limited to approved schemes. The model’s fluency is irrelevant if the application interprets part of the title as active markup.
Use harmless interpretation probes
Insert a recognizable inert markup-like string, an unsupported link scheme, a path containing a parent-directory component, and a command-shaped phrase in separate test outputs. Use isolated stubs for consumers that could execute or write. The goal is to observe interpretation without contacting an uncontrolled destination or changing a real system.
For a query consumer, test whether structured parameters remain parameters instead of becoming concatenated executable text. For a file writer, inspect the resolved destination. Keep each probe tied to a declared contract so a failure identifies a specific encoding, validation, or representation problem.
Inspect final effects and legitimate content
Capture the model output, transformed representation, consumer decision, and resulting artifact. A string can pass a pre-render scan while a later parser changes its meaning. Inspect the final rendered page or stub invocation, not only the first serialized response.
Include valid titles with punctuation, permitted links, and ordinary relative paths under the supported root. Overblocking these controls can make a system appear safe while breaking useful output. Report unintended interpretation, prohibited effects, false denials, and corrupted content separately; they often require different implementation fixes.
| Case | Evidence to retain | Acceptance condition |
|---|---|---|
| Markup-like title | Rendered page | Displayed as inert content |
| Unsupported link | Resolved destination | Rejected or safely omitted |
| Valid punctuation | Rendered control | Readable legitimate title |
Choose a boundary the application can enforce
Accept the report builder when generated titles remain text, allowed links work, and unsupported representations are rejected or displayed inertly. Use consumer-appropriate escaping and structured interfaces. A prompt asking for safe output can reduce problematic examples but cannot establish how a renderer or command wrapper will interpret them.
Retain the consumer version and final artifacts for regression review. Re-run after changing rendering libraries, query builders, or path handling. The acceptance statement should name tested consumers and representations rather than claiming that all generated content is safe in every application context.
Limits of the evidence
The probes are proposed for authorized isolated consumers and do not contain a live exploit target. No application was penetration-tested. Consumer-specific checks cannot establish universal output safety or replace review of the actual implementation.
Common questions
Can one sanitizer protect every consumer?
Different interpreters need context-appropriate representations and validation.
Should the model be the final safety check?
The application consumer should enforce its contract independently of generated instructions.
Sources & further reading
Primary sources behind this briefing. A source’s findings apply to its own study conditions; publication on arXiv does not establish peer review.
- OWASP LLM05:2025 Improper Output Handling OWASP · 2025 · Security guidanceReviewed: risk at downstream consumers of generated output; risk edition year retained. Accessed October 16, 2026.
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