diff --git a/packages/manager/.changeset/pr-13404-fixed-1771343065083.md b/packages/manager/.changeset/pr-13404-fixed-1771343065083.md
new file mode 100644
index 00000000000..ca3850c7668
--- /dev/null
+++ b/packages/manager/.changeset/pr-13404-fixed-1771343065083.md
@@ -0,0 +1,5 @@
+---
+"@linode/manager": Fixed
+---
+
+Fix html injection vuln in open Support Ticket and Quotas Increase Form ([#13404](https://github.com/linode/manager/pull/13404))
diff --git a/packages/manager/src/features/Account/Quotas/QuotasIncreaseForm.tsx b/packages/manager/src/features/Account/Quotas/QuotasIncreaseForm.tsx
index dff1302854d..f130a0bbdb8 100644
--- a/packages/manager/src/features/Account/Quotas/QuotasIncreaseForm.tsx
+++ b/packages/manager/src/features/Account/Quotas/QuotasIncreaseForm.tsx
@@ -14,6 +14,7 @@ import * as React from 'react';
 import { Controller, FormProvider, useForm } from 'react-hook-form';
 
 import { Markdown } from 'src/components/Markdown/Markdown';
+import { SUPPORT_TICKET_SANITIZE_OPTIONS } from 'src/features/Support/sanitizeOptions';
 
 import { getQuotaIncreaseFormSchema, getQuotaIncreaseMessage } from './utils';
 
@@ -254,7 +255,10 @@ export const QuotasIncreaseForm = (props: QuotasIncreaseFormProps) => {
                 {summary}
               </Typography>
               <Markdown textOrMarkdown={quotaIncreaseDescription} />{' '}
-              <Markdown textOrMarkdown={notes ?? ''} />
+              <Markdown
+                sanitizeOptions={SUPPORT_TICKET_SANITIZE_OPTIONS}
+                textOrMarkdown={notes ?? ''}
+              />
             </Stack>
           </Accordion>
           <ActionsPanel
diff --git a/packages/manager/src/features/Support/TicketDetailText.tsx b/packages/manager/src/features/Support/TicketDetailText.tsx
index 913c468c065..ed63d084fff 100644
--- a/packages/manager/src/features/Support/TicketDetailText.tsx
+++ b/packages/manager/src/features/Support/TicketDetailText.tsx
@@ -7,6 +7,8 @@ import { makeStyles } from 'tss-react/mui';
 
 import { Markdown } from 'src/components/Markdown/Markdown';
 
+import { SUPPORT_TICKET_SANITIZE_OPTIONS } from './sanitizeOptions';
+
 import type { Theme } from '@mui/material/styles';
 
 const useStyles = makeStyles()((theme: Theme) => ({
@@ -52,7 +54,10 @@ export const TicketDetailText = (props: Props) => {
   return (
     <Grid className={classes.root} container spacing={2}>
       <Grid style={{ width: '100%' }}>
-        <Markdown textOrMarkdown={ticketReplyBody} />
+        <Markdown
+          sanitizeOptions={SUPPORT_TICKET_SANITIZE_OPTIONS}
+          textOrMarkdown={ticketReplyBody}
+        />
       </Grid>
       {truncatedText !== text && (
         <IconButton
diff --git a/packages/manager/src/features/Support/sanitizeOptions.ts b/packages/manager/src/features/Support/sanitizeOptions.ts
new file mode 100644
index 00000000000..81fcdd35f72
--- /dev/null
+++ b/packages/manager/src/features/Support/sanitizeOptions.ts
@@ -0,0 +1,61 @@
+import type { SanitizeOptions } from 'src/utilities/sanitizeHTML';
+
+/**
+ * Centralized sanitization configuration for support ticket content
+ *
+ * This configuration is used when rendering user-submitted support ticket descriptions
+ * and replies via the Markdown component. It allows safe Markdown formatting while
+ * blocking dangerous HTML that could be used for phishing attacks.
+ *
+ * Security Policy:
+ * - Allows: Bold, italic, lists, code blocks, headers, tables, etc. (safe formatting)
+ * - Blocks: <a> tags and other potentially dangerous HTML elements
+ * - Preserves: Text content when removing disallowed tags
+ *
+ * Rationale:
+ * - Users expect Markdown formatting support for better readability
+ * - Links are blocked to prevent phishing/social engineering attacks
+ * - Sanitization happens at render time (not on submit) to preserve original content
+ */
+export const SUPPORT_TICKET_SANITIZE_OPTIONS: SanitizeOptions = {
+  ALLOWED_TAGS: [
+    // Text formatting
+    'strong',
+    'b',
+    'em',
+    'i',
+    'u',
+    'del',
+    's',
+    // Code blocks
+    'code',
+    'pre',
+    'span',
+    // Lists
+    'ul',
+    'ol',
+    'li',
+    // Structure
+    'p',
+    'br',
+    'hr',
+    'blockquote',
+    // Headers
+    'h1',
+    'h2',
+    'h3',
+    'h4',
+    'h5',
+    'h6',
+    // Tables
+    'table',
+    'thead',
+    'tbody',
+    'tr',
+    'th',
+    'td',
+    // NO <a> tags - links are blocked to prevent phishing
+  ],
+  ALLOWED_ATTR: ['class', 'style'], // Only for syntax highlighting in code blocks
+  KEEP_CONTENT: true, // Preserve text when removing disallowed tags
+};