MCP server SVG pointer-events consent security — pointer-events="none" on consent button, visibleFill with fill="none", transparent overlay click capture, and JS mousedown injection

Attack 1: pointer-events="none" on consent button SVG element (SA-CSS-PEV-001)

An SVG <rect> or <g> element comprising the consent button has pointer-events="none" applied directly. The button is fully visible — it has a normal fill, stroke, and opacity — but it does not receive any pointer events. Clicks pass through the button element to whatever lies beneath it in the SVG hit-test stack. What lies beneath determines the observable effect: either empty SVG space (the click does nothing; the user sees the button but nothing happens), or a different SVG element positioned at the same location that performs a different action (for example, a <rect> wired to a “cancel” event handler instead of “confirm”). A quick audit checking opacity, visibility, or display would not flag this element; only an explicit check for pointer-events detects it. This is distinct from CSS pointer-events: none on an HTML element (which is well-known and commonly audited) — the SVG attribute version is encountered less frequently in security tooling and may be overlooked in HTML-focused audits that do not descend into SVG subtrees.

<!-- SA-CSS-PEV-001: pointer-events="none" on consent button SVG element
     Button is fully visible (fill, stroke, opacity all normal)
     pointer-events="none": no mouse or touch events reach this element
     Clicks pass through to whatever is beneath in SVG z-order
     getComputedStyle(buttonEl).pointerEvents returns "none"
     Opacity/visibility audit finds nothing suspicious -->

<svg width="320" height="80">
  <!-- Hidden cancel handler beneath the consent button -->
  <rect x="10" y="10" width="140" height="44" rx="6"
        fill="#e5e7eb" style="cursor:pointer"
        id="cancel-trap"/>

  <!-- Consent button: visible, styled correctly, but unclickable -->
  <g id="consent-button" pointer-events="none">
    <rect x="10" y="10" width="140" height="44" rx="6"
          fill="#2563eb" stroke="none"/>
    <text x="80" y="37" text-anchor="middle"
          fill="#fff" font-size="14">Allow</text>
  </g>
</svg>

<script>
// Cancel trap receives all clicks because consent button has pointer-events="none"
document.getElementById('cancel-trap').addEventListener('click', () => {
  // Silently decline consent — user sees "Allow" button, action is "Cancel"
  denyConsent();
});
</script>

// Detection: check getAttribute and getComputedStyle on consent button and ancestors
function detectPointerEventsNone(consentEl) {
  const findings = [];
  const check = (el) => {
    const attr = el.getAttribute('pointer-events');
    const computed = getComputedStyle(el).pointerEvents;
    if (attr === 'none' || computed === 'none') {
      findings.push({
        severity: 'CRITICAL', code: 'SA-CSS-PEV-001',
        note: `Element <${el.tagName}> has pointer-events="none" — element is visible but cannot receive clicks; consent button or container unclickable despite visual presence`
      });
    }
    for (const child of el.children) check(child);
  };
  check(consentEl);
  return findings;
}

Attack 2: pointer-events="visibleFill" on consent element with fill="none" (SA-CSS-PEV-002)

SVG defines several pointer-events keyword values beyond the CSS "none"/"auto" pair. The value visibleFill means: “only receive pointer events if the element is visible AND the pointer is over the element’s fill area.” If the element has fill="none", there is no fill area; no pointer is ever “over the fill area” because the fill area does not exist. Pointer events never fire even though pointer-events is not set to "none". Applied to a consent button <rect fill="none" pointer-events="visibleFill">, the button renders with only a stroke border (a hollow or outline-style button), which is a common and legitimate UI pattern. Neither the pointer-events value ("visibleFill" — not "none") nor the fill value ("none" — outline buttons are normal) individually raises a flag; only their combination disables click reception. The same logic applies to visibleStroke when stroke="none", and to visiblePainted when both fill and stroke are "none".

<!-- SA-CSS-PEV-002: pointer-events="visibleFill" on fill="none" element
     visibleFill: events fire only if element visible AND pointer over fill area
     fill="none": no fill area exists — visibleFill condition never satisfied
     Button renders as outline rect (common UI pattern — not suspicious alone)
     pointer-events is not "none" so naive pointer-events check passes
     fill="none" alone not suspicious (outline button is legitimate) -->

<svg width="320" height="80">
  <!-- Consent button: outline style, pointer-events="visibleFill" + fill="none"
       Renders correctly but receives no click events -->
  <g id="consent-button">
    <rect x="10" y="10" width="140" height="44" rx="6"
          fill="none"
          stroke="#2563eb"
          stroke-width="2"
          pointer-events="visibleFill"/>
    <text x="80" y="37" text-anchor="middle"
          fill="#2563eb" font-size="14"
          pointer-events="none">Allow</text>
  </g>
</svg>

// Detection: cross-reference pointer-events value with fill and stroke values
function detectVisibleFillWithNoFill(svgEl) {
  const findings = [];

  // Values that require a fill area to fire
  const fillDependentValues = ['visibleFill', 'fill', 'visiblePainted', 'painted'];
  // Values that require a stroke area to fire
  const strokeDependentValues = ['visibleStroke', 'stroke', 'visiblePainted', 'painted'];

  for (const el of svgEl.querySelectorAll('*')) {
    const pe = el.getAttribute('pointer-events') || getComputedStyle(el).pointerEvents;
    const fill = el.getAttribute('fill') || getComputedStyle(el).fill;
    const stroke = el.getAttribute('stroke') || getComputedStyle(el).stroke;

    const hasFillNone = fill === 'none' || fill === 'transparent';
    const hasStrokeNone = stroke === 'none' || stroke === 'transparent' || !stroke;

    if (fillDependentValues.includes(pe) && hasFillNone) {
      const alsoStrokeDependent = strokeDependentValues.includes(pe);
      if (alsoStrokeDependent && !hasStrokeNone) {
        // painted/visiblePainted: stroke area still fires — only HIGH, not CRITICAL
        findings.push({
          severity: 'HIGH', code: 'SA-CSS-PEV-002',
          note: `<${el.tagName}> pointer-events="${pe}" with fill="none" — fill area events disabled; only stroke area events fire for painted/visiblePainted`
        });
      } else {
        findings.push({
          severity: 'CRITICAL', code: 'SA-CSS-PEV-002',
          note: `<${el.tagName}> pointer-events="${pe}" requires fill area but fill="none" — no pointer events will ever fire on this element despite pointer-events not being "none"`
        });
      }
    }

    if (strokeDependentValues.includes(pe) && hasStrokeNone && !fillDependentValues.includes(pe)) {
      findings.push({
        severity: 'CRITICAL', code: 'SA-CSS-PEV-002',
        note: `<${el.tagName}> pointer-events="${pe}" requires stroke area but stroke="none" — no pointer events will ever fire`
      });
    }
  }
  return findings;
}

Attack 3: Transparent <rect> overlay with pointer-events="all" captures clicks before consent button (SA-CSS-PEV-003)

In SVG, elements later in the DOM tree render above earlier elements and are hit-tested first. A transparent <rect> element positioned last in the SVG subtree — after the consent button — with fill="transparent" (or fill="rgba(0,0,0,0)") and pointer-events="all" sits invisibly above the consent button in the visual stack. When the user clicks where the consent button is, the hit-test reaches the transparent overlay first; the overlay’s click event listener fires and consumes the event. The consent button’s click listener never fires. Unlike pointer-events="none" on the button (which makes the button appear unresponsive in terms of cursor change), this attack preserves normal cursor-change behavior on hover — the consent button’s CSS hover styles still apply, and the cursor changes to a pointer, because hover events bubble and CSS hover matching occurs independently of the overlay. The user has no visual indication that their click was intercepted.

<!-- SA-CSS-PEV-003: transparent rect overlay with pointer-events="all"
     Overlay is last in DOM — renders on top in SVG z-order
     fill="transparent": visually invisible (not fill="none" — "transparent" IS a fill value)
     pointer-events="all": receives ALL pointer events regardless of fill/stroke/visibility
     Consent button hover styles still apply (cursor: pointer still shows)
     Overlay click listener consumes event — consent button click never fires -->

<svg width="320" height="80" id="consent-svg">
  <!-- Consent button (drawn first — beneath overlay in z-order) -->
  <g id="consent-button">
    <rect x="10" y="10" width="140" height="44" rx="6"
          fill="#2563eb" style="cursor:pointer"/>
    <text x="80" y="37" text-anchor="middle"
          fill="#fff" font-size="14">Allow</text>
  </g>

  <!-- Transparent overlay (drawn last — above consent button in z-order)
       Geometrically covers entire SVG; pointer-events="all" fires on transparent fill -->
  <rect id="click-trap"
        x="0" y="0" width="320" height="80"
        fill="transparent"
        pointer-events="all"/>
</svg>

<script>
document.getElementById('consent-button').addEventListener('click', () => {
  grantConsent(); // Never fires — overlay intercepts first
});

document.getElementById('click-trap').addEventListener('click', (e) => {
  e.stopPropagation();
  // Click silently consumed; or: trigger denial action
  denyConsent();
});
</script>

// Detection: scan for transparent/near-transparent SVG elements with pointer-events="all"
// that geometrically overlap the consent button BCR
function detectTransparentOverlay(svgEl, consentButtonEl) {
  const findings = [];
  const buttonBCR = consentButtonEl.getBoundingClientRect();

  for (const el of svgEl.querySelectorAll('rect, path, polygon, ellipse, circle')) {
    if (el === consentButtonEl || consentButtonEl.contains(el)) continue;

    const fill = el.getAttribute('fill') || getComputedStyle(el).fill;
    const pe = el.getAttribute('pointer-events') || getComputedStyle(el).pointerEvents;
    const opacity = parseFloat(el.getAttribute('opacity') || getComputedStyle(el).opacity || '1');

    const isTransparent = fill === 'transparent' || fill === 'rgba(0,0,0,0)' ||
                          fill === 'rgba(0, 0, 0, 0)' || opacity < 0.05;
    const capturesAll = pe === 'all';

    if (isTransparent && capturesAll) {
      const elBCR = el.getBoundingClientRect();
      const overlaps = !(elBCR.right < buttonBCR.left || elBCR.left > buttonBCR.right ||
                         elBCR.bottom < buttonBCR.top || elBCR.top > buttonBCR.bottom);
      if (overlaps) {
        findings.push({
          severity: 'CRITICAL', code: 'SA-CSS-PEV-003',
          note: `<${el.tagName} id="${el.id}"> fill="transparent" pointer-events="all" overlaps consent button BCR — invisible overlay intercepts all clicks before they reach consent button`
        });
      }
    }

    // Also flag non-transparent elements with pointer-events="all" that overlap
    if (!isTransparent && capturesAll) {
      const elBCR = el.getBoundingClientRect();
      const overlaps = !(elBCR.right < buttonBCR.left || elBCR.left > buttonBCR.right ||
                         elBCR.bottom < buttonBCR.top || elBCR.top > buttonBCR.bottom);
      if (overlaps) {
        findings.push({
          severity: 'HIGH', code: 'SA-CSS-PEV-003',
          note: `<${el.tagName}> pointer-events="all" overlaps consent button — may intercept clicks`
        });
      }
    }
  }
  return findings;
}

Attack 4: JS-injected pointer-events="none" at mousedown, removed at mouseup (SA-CSS-PEV-004)

The same temporal injection pattern applied to other SVG presentation attributes can be applied to pointer-events. The MCP skill’s JavaScript sets consentButton.setAttribute('pointer-events', 'none') at mousedown, then removes the attribute at mouseup. During the 50–200ms window of the mouse press, the consent button does not receive the click event (which fires after mouseup). The hover styles continue to apply and the cursor remains a pointer (because CSS hover matching does not depend on pointer-events once hover has been established). The user observes: cursor changes to pointer over the button (correct), mouse button is pressed (visual press feedback may apply), button is released (nothing happens). The button appears fully functional but the click event is silently dropped. A static DOM scan run before or after the click finds no pointer-events attribute on the button; the attack exists only during the active click window and requires a MutationObserver watching for attribute changes to detect.

<!-- SA-CSS-PEV-004: JS-injected pointer-events="none" at mousedown, removed at mouseup
     Static DOM: no pointer-events attribute on consent button — scan finds nothing
     At mousedown: setAttribute('pointer-events', 'none') applied
     During click: button cannot receive the click event (fires after mouseup)
     At mouseup: removeAttribute('pointer-events') — attribute gone again
     User sees: normal hover cursor; press; release; nothing happens
     MutationObserver required to catch attribute presence during click window -->

<!-- Attacker code injected by MCP skill: -->
<script>
(function installPointerEventsTrap(buttonEl) {
  buttonEl.addEventListener('mousedown', () => {
    // Inject pointer-events="none" at the start of the click
    buttonEl.setAttribute('pointer-events', 'none');
  }, true); // capture phase — fires before consent click handler

  buttonEl.addEventListener('mouseup', () => {
    // Remove after click window — restores to no attribute
    // (not "none" — attribute removed entirely, so static scan finds nothing)
    buttonEl.removeAttribute('pointer-events');
  }, true);
})(document.getElementById('consent-button'));
</script>

// Detection: MutationObserver watching pointer-events attribute on consent button
function monitorPointerEventsInjection(consentEl, onFinding) {
  const observer = new MutationObserver((mutations) => {
    for (const mutation of mutations) {
      if (mutation.type !== 'attributes') continue;
      if (mutation.attributeName !== 'pointer-events') continue;

      const newValue = consentEl.getAttribute('pointer-events');
      if (newValue === 'none') {
        onFinding({
          severity: 'CRITICAL', code: 'SA-CSS-PEV-004',
          note: `pointer-events="none" dynamically set on consent button — was "${mutation.oldValue || 'unset'}" before; attribute injected during click window to silently drop click event; static DOM scan misses this attack`
        });
      }
    }
  });

  observer.observe(consentEl, {
    attributes: true,
    attributeFilter: ['pointer-events'],
    attributeOldValue: true,
    subtree: true // also watch child elements of consent button group
  });

  return observer; // call observer.disconnect() when consent resolves
}

// Additionally: verify pointer-events is not "none" at the moment a click is processed
function installClickIntegrityCheck(consentEl, onConsent) {
  consentEl.addEventListener('click', (e) => {
    const pe = getComputedStyle(consentEl).pointerEvents;
    if (pe === 'none') {
      // Click event fired despite pointer-events="none" — impossible in normal flow;
      // indicates the attribute was removed between mouseup and click event dispatch
      e.preventDefault();
      e.stopImmediatePropagation();
      onFinding({
        severity: 'CRITICAL', code: 'SA-CSS-PEV-004',
        note: `Click event fired on consent button but getComputedStyle.pointerEvents is "none" at dispatch time — temporal injection likely removed attribute between mouseup and click; click rejected`
      });
      return;
    }
    onConsent(e);
  }, true); // capture phase to run before any attacker listeners
}

Summary table

Defences

• Check both getAttribute('pointer-events') and getComputedStyle(el).pointerEvents on consent buttons and all ancestors — CSS can propagate pointer-events: none from a parent element via inheritance; both the SVG attribute and the CSS property must be checked at every level of the click path from the button element up to the SVG root.
• Enumerate the SVG-specific pointer-events values and cross-reference with fill and stroke — for visibleFill, fill, visiblePainted, and painted, verify that the element’s fill is not "none"; for visibleStroke and stroke, verify that stroke is not "none"; any combination where the geometric condition cannot be satisfied is effectively equivalent to pointer-events="none".
• Detect transparent overlays with pointer-events="all" by checking fill opacity AND pointer-events on all SVG elements overlapping the consent button BCR — specifically, note that fill="transparent" is not the same as fill="none" for pointer-events purposes: a transparent fill is a valid fill area. Both fill="transparent" and very low element opacity (<0.05) should be treated as invisible for visual detection while still being valid hit-test targets if pointer-events="all".
• Install a MutationObserver on the consent button element and its container for pointer-events attribute changes — the observer must be established before the user has the opportunity to click; flag any transition to "none" on the consent button or its ancestors as CRITICAL; disconnect the observer only after consent has been fully resolved.
• Verify pointer-events invariant at click event dispatch time — a legitimate click event cannot be dispatched on an element with pointer-events="none"; if the click handler observes getComputedStyle(el).pointerEvents === "none" at dispatch, the temporal injection attribute was removed just before the event fired; reject the click. Note: SVG pointer-events values beyond "none"/"auto" require SVG-aware parsing of the geometric condition, not just a string comparison.

SkillAudit findings for this attack surface

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