Cross-site scripting lets an attacker run their code in your users' browsers — stealing sessions, keystrokes and data. This is dedicated XSS testing that goes past pattern-matching to craft context-aware payloads for reflected, stored and DOM-based variants, as one focused part of a full web application penetration test.
The hard part of XSS is context: the same input may be safe in one place and exploitable in another. We test each injection point in its actual output context — HTML, attribute, JavaScript, URL — and evaluate any CSP to see whether it truly contains an attack.
DOM-based XSS is invisible to server-side scanners because the flaw lives in client JavaScript — exactly where modern apps put more and more logic. Finding it takes reading the front-end, not just fuzzing the back-end.
What we test
Reflected XSS across every input and context
Stored/persistent XSS in saved content
DOM-based XSS in client-side JavaScript
Mutation XSS (mXSS) and parser quirks
Filter, encoder and WAF bypass
Content-Security-Policy (CSP) evaluation
Common vulnerabilities we uncover
Session hijacking via stored XSS
Credential and keystroke theft
DOM-based XSS in single-page apps
Account takeover through script injection
CSP misconfiguration and bypass
Phishing and UI redressing via injection
Our methodology
Scoping & rules of engagement. We agree objectives, targets and boundaries for your cross-site scripting (xss) testing, so testing is safe, authorized and focused on what matters to your business.
Reconnaissance & mapping. We enumerate the full attack surface in scope, building a complete picture before any exploitation begins.
Manual exploitation. Our senior testers chain vulnerabilities by hand — going far beyond automated scanners — to prove real, demonstrable impact.
Analysis & reporting. Every finding is triaged, risk-rated with CVSS and written up with a copy-paste reproduction and clear remediation.
Remediation support & free retest. We support your team through the fixes and retest the remediated issues to confirm they are genuinely closed.
Tools & techniques
We work by hand, crafting payloads for the specific sink and encoding in play and bypassing filters where they are weak, then proving impact with a benign but unmistakable demonstration. DOM XSS is hunted by reading the JavaScript, not guessing at it.
For client-heavy apps this pairs with our SPA penetration testing, and it sits within full web application penetration testing for end-to-end coverage.
When you need this engagement
Your app reflects or stores user-controlled content
You run a JavaScript-heavy or single-page front-end
You rely on a WAF or filter you want validated
You handle sessions or sensitive actions in-browser
You need confirmed, exploitable proof of XSS
What you receive
Confirmed XSS findings with working payloads
Context and sink documented per finding
Output-encoding and CSP remediation guidance
Reproduction steps for developers
Attestation letter where required
Complimentary retest after fixes
What’s included in your report
Every cross-site scripting (xss) testing engagement concludes with a comprehensive, board-ready report and a working session to walk your team through it. Your report includes:
An executive summary with overall risk posture for non-technical stakeholders
Detailed technical findings, each with a step-by-step, copy-paste reproduction
CVSS v3.1 severity ratings and business-impact context for every issue
Prioritized, actionable remediation guidance your engineers can apply directly
A complimentary retest to confirm fixes and update finding status
A formal attestation letter for customers, auditors and compliance programs
Standards & frameworks
OWASP Top 10 A03: InjectionOWASP WSTGCWE-79Content Security Policy Level 3
Outcomes you can expect
After your cross-site scripting (xss) testing, you will have clear, evidence-based visibility into your real security risk — not a scanner’s guesswork. You will know exactly which weaknesses an attacker could exploit, what the business impact would be, and the precise steps to fix them in priority order. Teams use our findings to close critical gaps, satisfy customer and regulator security requirements, and demonstrate due diligence to their board. With a complimentary retest included, you also get documented proof that the issues are genuinely resolved.
Engagement details & logistics
Every cross-site scripting (xss) testing starts with a short, no-obligation scoping call to understand your goals, environment and constraints, followed by a fixed-price proposal and a clear statement of work. Most engagements are delivered fully remotely, with on-site work arranged where it genuinely adds value. Throughout testing we maintain an agreed communication cadence and escalate any critical, high-impact finding to you immediately rather than waiting for the final report. All work is performed under a signed NDA with strict data-handling controls, using safe, non-disruptive techniques and carefully coordinated rules of engagement to protect your production systems. On completion you receive your report and a walkthrough session, followed by a complimentary retest once your fixes are in place. Typical engagements are booked one to three weeks in advance, and urgent or pre-deadline testing can often be accommodated — just ask at hi@agentoffense.com.
Why organizations choose AgentOffense
Our cross-site scripting (xss) testing is delivered by senior offensive-security engineers who test the way real attackers do — manually, creatively and with a relentless focus on proving genuine, demonstrable impact. Here is what sets our engagements apart:
Manual, exploit-driven testing that chains vulnerabilities the way a real attacker would, going far beyond what automated scanners can find.
Reproducible proof for every finding, with copy-paste reproduction steps your engineers can follow and independently verify.
Honest severity calibration so you invest in fixing what genuinely matters and avoid wasting effort on false positives and noise.
Clear, business-focused reporting that speaks to engineers and executives alike, tying every issue to real-world impact.
A complimentary retest included, so you get documented proof that your fixes actually close the attack path.
Responsible, collaborative delivery with a named point of contact and secure handling of all data throughout the engagement.
Explore related services
Cross-Site Scripting (XSS) Testing is frequently scoped alongside our other offensive-security services for broader coverage. Explore related engagements that complement it:
Web Application Penetration Testing — Manual web application penetration testing against the OWASP Top 10 and business-logic flaws. Exploit-driven testing with…
OWASP Top 10 Penetration Testing — OWASP Top 10 penetration testing — manual, exploit-led assessment against every OWASP risk category.
How much does Cross-Site Scripting (XSS) Testing cost?
Every cross-site scripting (xss) testing is scoped and priced individually, so you pay for exactly the coverage you need — with no hidden extras. After a short, no-obligation scoping call we send a fixed-price quote, usually within one business day, with clear deliverables, a firm timeline and a complimentary retest included. The price of your cross-site scripting (xss) testing depends on the size and complexity of the target and the depth of testing required, so you always know the cost up front before any work begins.
