CVE-2026-45502 Overview
CVE-2026-45502 is a Server-Side Request Forgery (SSRF) vulnerability in Microsoft Exchange Server. An authenticated attacker can abuse the flaw to coerce the Exchange Server into issuing requests on the attacker's behalf and disclose information over a network. The weakness is classified under CWE-918. Microsoft published mitigation guidance through its Microsoft Security Update CVE-2026-45502 advisory. The CVSS 3.1 base score is 5.0, reflecting low privileges required, no user interaction, and a scope change leading to limited confidentiality impact.
Critical Impact
An authenticated attacker can force Exchange Server to make network requests on its behalf, enabling disclosure of information accessible from the server's network position.
Affected Products
- Microsoft Exchange Server (refer to the Microsoft advisory for supported, patched build numbers)
Discovery Timeline
- 2026-06-09 - CVE-2026-45502 published to NVD
- 2026-06-09 - Last updated in NVD database
Technical Details for CVE-2026-45502
Vulnerability Analysis
The issue is a Server-Side Request Forgery weakness in Microsoft Exchange Server. Exchange exposes several HTTP endpoints that fetch or proxy resources based on user-supplied input. When such an endpoint fails to validate the target of a server-initiated request, an authenticated user can direct Exchange to connect to arbitrary internal or external destinations. The CVSS vector indicates a scope change, meaning the impact crosses the authorization boundary of the Exchange component. The attacker needs valid credentials but not administrative privileges, and no user interaction is required. The flaw maps to CWE-918: Server-Side Request Forgery. The EPSS probability is 0.062% at the time of publication, indicating limited observed exploitation activity.
Root Cause
The root cause is insufficient validation of URLs or hostnames processed by an Exchange server-side component that issues outbound requests. Without enforcing an allowlist of permitted destinations or stripping internal addresses, the server treats attacker-controlled targets as legitimate.
Attack Vector
The attack vector is network-based. An authenticated user sends a crafted request to a vulnerable Exchange endpoint that accepts a URL or resource reference. Exchange then connects to the supplied destination using its own identity and network position, returning response data or metadata that the attacker can read. Because the scope changes, the disclosed information can include data the authenticated user would not normally access. No verified public proof-of-concept code is currently available; consult the Microsoft advisory for technical specifics.
Detection Methods for CVE-2026-45502
Indicators of Compromise
- Unexpected outbound HTTP or HTTPS connections originating from Exchange Server processes such as w3wp.exe to internal management interfaces or cloud metadata endpoints.
- IIS logs on Exchange showing authenticated requests containing URL-like parameters that reference internal IP addresses, localhost, or non-Exchange hostnames.
- Anomalous DNS queries from Exchange servers resolving hostnames not associated with normal mail flow or hybrid connectivity.
Detection Strategies
- Inspect Exchange IIS logs for requests where user-supplied parameters contain URL schemes (http://, https://, file://) targeting non-standard hosts.
- Correlate authenticated Exchange sessions with subsequent outbound network connections to detect server-initiated requests that follow user actions.
- Compare baseline outbound traffic from Exchange servers against current behavior to surface new destinations reached by the Exchange application pool identity.
Monitoring Recommendations
- Forward IIS, Exchange, and Windows Security event logs to a centralized analytics platform and alert on outbound connections from Exchange to internal management subnets.
- Monitor for repeated authentication followed by parameterized requests referencing URLs, which is characteristic of SSRF probing.
- Track changes to Exchange virtual directory configuration and any newly registered HTTP modules or handlers.
How to Mitigate CVE-2026-45502
Immediate Actions Required
- Apply the security update referenced in the Microsoft Security Update Guide for CVE-2026-45502 to all affected Exchange Server roles.
- Audit Exchange Server accounts and revoke unnecessary mailbox or service credentials, since exploitation requires authentication.
- Restrict outbound network access from Exchange servers to only the destinations required for mail flow, hybrid connectivity, and management.
Patch Information
Microsoft has published the official fix through the Microsoft Security Update Guide. Administrators should review the advisory for the cumulative update or security update applicable to their Exchange Server build and install it on every server in the organization, including edge transport and hybrid servers.
Workarounds
- Place Exchange servers behind an egress proxy or firewall that blocks connections to internal management ranges and cloud metadata services such as 169.254.169.254.
- Limit access to Exchange web services and management endpoints to trusted client networks using IP-based restrictions in IIS.
- Enforce multi-factor authentication on all Exchange-facing accounts to raise the cost of obtaining the credentials required for exploitation.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
