Prompt Injection Testing
Prompt injection is the SQL injection of the LLM era. We test your application for direct and indirect injection, system-prompt leakage and the data exfiltration they enable.
What is Prompt Injection Testing?
Prompt injection is the injection bug of the LLM era, and it can't be fully patched — only contained. We test your application for direct and indirect injection, system-prompt leakage and the data exfiltration they enable, then show what an injection can actually reach.
Prompt injection is the defining vulnerability class of LLM applications, and like injection bugs before it, its danger is in what it reaches. An injection can leak your system prompt, exfiltrate data, or — when model output is rendered or fed downstream — become XSS or trigger an action. We test for direct and indirect injection and then trace each one to real impact, so you know which are cosmetic and which are serious.
Prompt injection testing also clarifies a truth teams find uncomfortable: you cannot filter your way to safety, because the model can't reliably distinguish instructions from data. The realistic goal is containment — limiting what an injection can reach and do — and testing is how you discover whether your architecture actually contains it or merely hopes to.
Prompt Injection Testing is a manual, exploit-driven assessment: real people attacking your target the way an adversary would, then proving each finding with a working proof of concept. It is not an automated scan with a logo on it — the point is to find and demonstrate the issues that actually put you at risk, and hand your team a clear plan to fix them.
Why it matters
AI systems introduce an entirely new attack surface on top of the classic ones. Prompt injection, unsafe tool use and data leakage are already being exploited in production, and traditional testing doesn't cover them.
A prompt injection testing engagement replaces guesswork with evidence. Instead of hoping your controls hold, you get a ranked, reproducible picture of where they don’t — before someone hostile finds the same gaps.
Industries & use cases
Prompt injection testing matters for any LLM-powered feature — chatbots, assistants, summarisers, RAG apps, agents — especially those handling multiple users' data or connected to tools.
What we test
Manual, exploit-driven coverage focused on real impact — not scanner noise.
- Direct prompt injection
- Indirect injection via content/RAG
- System-prompt and instruction leakage
- Data exfiltration through the model
- Output-handling and downstream abuse
- Guardrail evasion techniques
Signs you should run a prompt injection testing
If any of these apply, testing is overdue.
- You've built any LLM-powered feature
- The model handles multiple users' data
- Model output is rendered, executed or fed to tools
- You rely on prompt-based guardrails alone
- You've never tested injection against your app
Common vulnerabilities we find
The issues that show up again and again in prompt injection testing — and the ones that actually get exploited.
Direct injection
User input overriding the system prompt or policy.
Indirect injection
Malicious instructions in retrieved or ingested content.
System-prompt leakage
Coaxing the model to reveal hidden instructions and data.
Injection-to-XSS via unescaped output
Model output rendered in a page without escaping, turning injection into stored XSS.
Cross-context data leakage
Injected instructions pulling data from other users, tools or sessions.
Instruction override of system prompt
User input taking priority over intended instructions and policy.
Data exfiltration via model output
Coaxing the model to emit secrets or other users' data.
Injection triggering downstream actions
Model output causing side effects in connected tools or systems.
Example attack chain
Real impact rarely comes from one bug — it comes from chaining several. A representative example:
Why choose webhook.press
Attacker mindset
We’re offensive security people who also build the free tools bug-bounty hunters use daily. We test the way real adversaries do — and prove it.
No scanner theatre
You get findings a human exploited and verified, ranked by real business risk — not an unfiltered tool dump padded to look thorough.
Fixed price, free retest
A clear quote after scoping, a report your team and auditors can use, and a free retest to confirm the fixes hold.
Our methodology
A structured, transparent process aligned to OWASP and PTES — with a named point of contact throughout.
Scoping & rules of engagement
We agree the exact targets, depth, timing and constraints for your prompt injection testing, and set clear rules of engagement so testing is safe and predictable.
Reconnaissance & mapping
We enumerate the full attack surface — endpoints, roles, technologies and trust boundaries — and threat-model where an attacker would focus.
Manual testing & exploitation
We attack by hand, verifying and chaining weaknesses into real impact. Automated tooling supports coverage; humans find the logic and authorization bugs it can’t.
Analysis & risk rating
Each finding is validated, rated by real business risk rather than raw scanner severity, and de-duplicated so you get signal, not noise.
Reporting
You receive an executive summary for leadership and a technical section with reproducible PoCs, evidence and concrete, stack-specific remediation.
Free retest
After you remediate, we re-test the closed findings to confirm they are actually fixed — at no extra cost.
What you get
Reproducible PoCs
Every finding ships with a working proof and step-by-step reproduction your engineers can replay and verify.
Risk-ranked findings
Prioritised by real business impact, so you fix what matters first instead of drowning in low-severity noise.
Actionable remediation
Concrete, stack-specific fixes and guidance — not generic “apply best practice” filler.
Free retest
We re-check the closed findings after remediation and confirm they’re resolved.
The report is written for two audiences at once: an executive summary that a non-technical stakeholder can act on, and a detailed technical section — findings, evidence, CVSS and reproduction — that your developers and auditors can use directly.
Manual testing, not just a scan
Automated scanners are fast and useful for coverage, but they only find patterns they already know, and they flood you with false positives. They cannot understand your business logic, chain several small issues into a breach, or tell you which alert actually matters. Our prompt injection testing is led by experienced testers who exploit findings by hand and rank them by the damage they’d really do — the difference between a 300-page tool dump and a short list of things worth fixing.
Standards & compliance
Our prompt injection testing reports are written to support the frameworks your auditors and customers care about — including SOC 2, ISO 27001, PCI DSS, HIPAA, GDPR, and the EU’s NIS2 and DORA. Each engagement produces clear, independent evidence of testing with scope, methodology and findings documented the way assessors expect, so the same test both hardens your systems and helps satisfy your obligations.
Frameworks we follow
Recognised methodologies, adapted to your target — never a rigid checklist.
- OWASP — Web Security Testing Guide, ASVS and the API Security Top 10
- PTES — the Penetration Testing Execution Standard
- NIST SP 800-115 — technical guide to security testing
- OSSTMM — Open Source Security Testing Methodology Manual
- MITRE ATT&CK — to frame real-world adversary techniques
FAQ
Direct vs indirect injection?
Direct is user input to the model; indirect hides instructions in content the model later reads (a page, a file, a webhook). We test both.
Can prompt injection be fully fixed?
Not entirely — but impact can be contained. We focus on what an injection can actually reach and do.
What's the difference between direct and indirect injection?
Direct is user input to the model; indirect hides instructions in content the model later reads — a page, a file, a webhook. We test both.
Do you test output handling too?
Yes — how the app renders and uses model output is often where injection becomes truly dangerous.
Can filtering fully stop prompt injection?
No — the realistic goal is containment. We test what an injection can reach and how to limit it.
Do you test both input and output paths?
Yes — output handling is often where injection becomes truly dangerous, so both are in scope.
How long does a prompt injection testing take?
Most focused engagements run one to two weeks depending on scope; we agree the exact timeline during scoping.
Is a retest included?
Yes — after you remediate, we re-check the closed findings to confirm they’re fixed, at no extra cost.
How do you price it?
Per engagement, based on scope and depth — you get a fixed quote after a short scoping call. No cookie-cutter packages.
Why teams trust our prompt injection testing
Aligned to recognised standards
Testing follows OWASP, PTES, NIST SP 800-115 and MITRE ATT&CK, and reports support SOC 2, ISO 27001, PCI DSS, HIPAA, GDPR, NIS2 and DORA.
Every engagement includes
Reproducible PoCs, risk-ranked findings, concrete remediation, a named point of contact, a free retest, and a summary letter of attestation.
Confidential by default
Work is covered by an NDA, scoped with clear rules of engagement, and data is handled with care throughout — including residency requirements.
Sample report available on request — see our reporting format and depth before you commit. Ask for a sample →
Get a quote for Prompt Injection Testing
Tell us about the target — we’ll come back with scope and a fixed price. Manual, exploit-driven testing with reproducible proof and a free retest.