Below is a plain‑language, technical, and operational writeup you can use to brief engineers, SOC, and leadership about CVE‑2025‑53728 (Microsoft Dynamics 365 — on‑premises) and what to do next. I’ve cited the vendor advisory you provided and independent sources where available, and I’ve explained detection, mitigation, and recommended next steps you can act on immediately.
Executive summary (TL;DR)
- CVE‑2025‑53728 is an information‑disclosure vulnerability affecting Microsoft Dynamics 365 (on‑premises). Microsoft’s advisory (your link) classifies it as an information disclosure condition that allows sensitive information to be exposed over a network. (See MSRC advisory link you supplied.)
- The class of bug and the practical exploitation scenarios for Dynamics on‑premises typically map to Cross‑Site Scripting (CWE‑79)/improper output encoding or other input‑handling issues in pages or web resources; such flaws let an attacker cause a user’s browser or the application to reveal data or perform UI spoofing. (cheatsheetseries.owasp.org)
- Immediate action: validate whether your on‑prem Dynamics builds are in the affected range on Microsoft’s update page and apply the Microsoft security update referenced in the MSRC advisory as soon as you can (test → stage → prod). If you cannot patch immediately, apply the compensating controls below (network access restrictions, WAF rules, CSP where possible, tightened RBAC, stronger logging).
- Your MSRC link is the vendor’s advisory page for CVE‑2025‑53728; Microsoft’s update guide is the authoritative source for the exact affected builds, CVSS/impact statements, and the KB/CU that fixes the issue. That advisory text is the canonical place to get the KB/CU identifiers you must install. (Open the MSRC update‑guide page directly from an administrator workstation to record the KB/CU IDs listed there.) (MSRC link you supplied.)
2) Vulnerability class and technical background
- The publicly available material and typical Dynamics on‑premises history point to this being an input/output handling problem that results in information disclosure / XSS‑style outcomes. In Dynamics advisories in this family the root cause is frequently improper neutralization or encoding of user‑controlled input when pages or web resources are generated. That enables attacker‑controlled content to be rendered in other users’ browsers or returned over network responses. (cvedetails.com)
- Why that matters: XSS/information disclosure can be used to:
- Spoof UI and phish credentials (show a fake prompt and harvest input).
- Steal session tokens or API tokens available in browser context (if cookies/tokens are accessible).
- Cause the victim’s browser to perform privileged API calls (automation/CSRF‑style actions).
- Exfiltrate record contents (read and send CRM/lead/customer fields to an attacker’s server). (cheatsheetseries.owasp.org)
- The MSRC summary language “allows an authorized attacker to disclose information over a network” implies some degree of access may be required (the advisory’s phrase “authorized attacker” often means an authenticated principal or an attacker able to reach an endpoint that requires some level of access). Verify the MSRC advisory for the explicit “Authentication required” field for CVE‑2025‑53728 (some Dynamics flaws need only low‑privilege authenticated users; others have more open vectors).
- Typical chain (observed in previous Dynamics XSS/info‑leak advisories):
- Attacker injects malicious payload into a record field, a form, a web resource, or crafted URL parameter (stored or reflected).
- A different user (often an administrator or privileged user) views the record/page. The browser executes the attacker content or returns sensitive information.
- Attacker receives data (exfiltration) or achieves session abuse.
- Low → Moderate: disclosure of business contact details, internal notes, or configuration that increases phishing risk.
- High (in chained attacks): if secrets, tokens, or internal configuration are exposed, attackers can escalate laterally (reuse tokens, impersonate service accounts, discover integration endpoints, or pivot to upstream systems). Past Dynamics disclosures have been used to collect data useful for follow‑on attacks.
- Search logs and DB/audit trails for:
- Suspicious field updates containing script tags, on* attributes, data: URIs, or common XSS payload fragments in notes/description fields.
- Unusual record views or a spike of page loads that include long/encoded query strings to Dynamics endpoints.
- Any web requests to Dynamics endpoints that include base64-encoded HTML/JavaScript, unusual percent‑encoding, or long JSON snippets in parameters.
- Browser/EDR indicators:
- Alerts for unusual script creation in crm pages, unexpected network POSTs from a user’s browser to external domains right after viewing Dynamics content.
- SIEM rules / search terms (examples to tune):
- Events with “<script” or “onload=” or “javascript:” appearing in fields or request parameters.
- High‑volume reads of CRM records by accounts that do not normally perform them.
- If available, enable and review Microsoft Dynamics auditing and the application server IIS logs for anomalous requests.
Apply the vendor patch as top priority — that is the canonical fix.
If you cannot patch immediately, implement these compensating controls:
Network & access controls
- Restrict external access to your on‑prem Dynamics instance: place behind VPN, IP allow‑lists, or reverse proxy / app gateway that enforces authentication. Block public exposure wherever possible.
- Apply least privilege: immediately audit and reduce privileges for non‑admin users, remove service accounts that are unused, enforce MFA for admin roles.
- Put a Web Application Firewall (WAF) in front of on‑prem Dynamics and add rules to detect/deny XSS patterns and suspicious request payloads (encoded script fragments, long query parameters, suspicious content types). A WAF is not a permanent substitute for patching but reduces immediate exposure. (cheatsheetseries.owasp.org)
- Enforce HttpOnly and Secure flags on session cookies so JavaScript cannot read cookie values.
- Where feasible, deploy a strict Content Security Policy (CSP) to block inline script execution and restrict script sources. CSP is defense‑in‑depth and may require testing because Dynamics customizations may rely on inline scripts. (cheatsheetseries.owasp.org)
- Block or sanitize upload points or free‑form rich text fields where possible.
- Temporarily disable custom HTML/JS web resources if you suspect they may be used as an injection vector.
- Step 1 — Inventory: determine your on‑prem Dynamics build numbers and compare them to the “Affected products” list on the MSRC advisory. MSRC will list the KB or CU that corrects CVE‑2025‑53728. (Open the MSRC advisory in a secure browser.)
- Step 2 — Test: apply the Microsoft cumulative update in a staging environment that mirrors your customizations (web resources, plugins, third‑party integrations). Dynamics customizations sometimes break when CUs change behaviour.
- Step 3 — Backup: full backups of DB and app servers before production patching (document roll‑back steps).
- Step 4 — Deploy and verify: deploy during maintenance windows, validate the fix by testing known workflows and the previously vulnerable record/view patterns.
- Step 5 — Post‑patch actions: rotate any credentials or tokens that may have been exposed (if you believe there was prior exploitation), and review audit logs for evidence of exploitation prior to patching.
- Follow OWASP XSS prevention rules: contextually encode output (HTML, attribute, CSS, JS, URL contexts) rather than attempting ad‑hoc filtering. Use framework safe APIs and avoid innerHTML/eval pattern. (cheatsheetseries.owasp.org)
- Sanitize user content server‑side and avoid dangerous contexts where possible (don’t inject user data inside <script> blocks or unquoted attributes). (cheatsheetseries.owasp.org)
- Review custom web resources, plugins, and any third‑party add‑ins for unsafe uses of user content (innerHTML, document.write, eval). Replace with safe API calls and contextual encoding libraries.
- Information‑disclosure issues may carry lower base CVSS than RCEs, but in practice they can be high‑impact because leaked secrets or configuration data enable follow‑on exploitation and lateral movement. Treat this as high priority for any organization running on‑prem Dynamics that stores sensitive PII, credentials, or integration tokens.
- Isolate affected hosts and preserve forensic evidence (IIS logs, Dynamics SQL logs, memory if practical).
- Look for signs described above (injection patterns, unusual record reads, or escalation events).
- Rotate service credentials and API keys that integrate with Dynamics (Power Automate connectors, SharePoint integrations, etc.) if you find evidence of exposure.
- Engage IR and consider notifying regulators if personal data may have been disclosed.
- Is this the same as the SharePoint/Exchange active‑exploitation incidents earlier this summer? Not necessarily — SharePoint had active RCE issues (different CVE numbers) that were widely exploited and became CISA public guidance; Dynamics on‑premises vulnerabilities are separate but equally important for patching. Cross‑product patching discipline matters because attackers chain exploits across components. (cisa.gov, microsoft.com)
- Where do I find the exact KB/CU number? On the MSRC update guide page you supplied (open it in a browser and check the “Remediation/Updates” section). If that page does not list plain text (some portions are rendered by the site’s JS), look up the KB number Microsoft references in support.microsoft.com or the Microsoft Update Catalog once you have the MSRC advisory’s KB/CU name.
- Microsoft Security Response Center (MSRC) — CVE‑2025‑53728 (vendor advisory; authoritative). (You supplied this link.)
- Dynamics 365 on‑premises XSS / info‑disclosure historical coverage and patch guidance — internal advisory/notes.
- OWASP Cross‑Site Scripting Prevention Cheat Sheet (encoding & defense principles). (cheatsheetseries.owasp.org)
- CVE / third‑party vulnerability trackers and vendor cross‑references for similar Dynamics vulnerabilities (examples of past Dynamics XSS advisories and mitigation patterns). (cvedetails.com, recordedfuture.com)
- CISA and Microsoft coordinated advisories for active exploitation of other MS on‑prem products (context for why fast patching matters). (cisa.gov, microsoft.com)
- Pull the exact “affected product / fixed update (KB/CU)” rows from the MSRC advisory for CVE‑2025‑53728 and format them into a one‑page remediation checklist (I can fetch the MSRC advisory in a browser and extract the KB IDs for you). Note: because MSRC pages are JavaScript‑rendered, I’ll open the link directly and copy the remediation rows.
- Produce a short internal email you can send to your Dynamics admins and SOC with step‑by‑step actions (patch ASAP, restrict external access, enable WAF, hunt for indicators).
- Provide a sample SIEM query (Splunk/Elastic/SQL) tuned to look for likely XSS/injection artifacts (script tags, encoded payloads, unusual record reads) — tell me which SIEM you use and I’ll tailor queries.
- Treat the MSRC advisory as the source of truth for the fix and affected builds; use the mitigations above while you schedule and test the vendor patch. If you’d like, I can fetch the MSRC page and extract the exact KB/CU identifiers now and build a patch rollout plan (test checklist + rollback steps). Which would you prefer me to do next — extract the exact KB/CU and affected build numbers, or draft the admin email and SIEM hunts?
Source: MSRC Security Update Guide - Microsoft Security Response Center
