Raw vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:LCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-26137 is a critical-severity SSRF (CWE-918) vulnerability in Microsoft 365 Copilot Chat. Its CVSS base score is 9.9 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 43th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-4 (Information Flow Enforcement) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-26137 is a server-side request forgery (SSRF) vulnerability, classified under CWE-918, affecting Microsoft Exchange. Published on 2026-03-19, it carries a CVSS v3.1 base score of 9.9, indicating critical severity due to its network accessibility (AV:N), low attack complexity (AC:L), and potential for high impact on confidentiality (C:H) and integrity (I:H) with a changed scope (S:C).
An authorized attacker with low privileges (PR:L) can exploit this SSRF vulnerability over the network without user interaction (UI:N), achieving privilege escalation. Successful exploitation allows the attacker to perform actions beyond their initial permissions, potentially compromising the Exchange server and accessing sensitive data or executing unauthorized operations.
The Microsoft Security Response Center (MSRC) provides detailed guidance on this vulnerability, including patch information and mitigation steps, at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-26137. Security practitioners should consult this advisory for deployment instructions and workarounds if applicable.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-13184
Vulnerability Data
Server-side request forgery (ssrf) in Microsoft Exchange allows an authorized attacker to elevate privileges over a network.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.3.6V1.5.3V5.3.2V10.4.7
Mitigating Controls (NIST 800-53 r5) AI
Information flow enforcement can restrict which destinations the server is allowed to contact on behalf of users.
Input validation directly stops untrusted URLs from being accepted and fetched without destination checks.
Boundary protection limits the network reach of server-initiated requests even if SSRF occurs.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure development practices directly include input validation and destination allow-listing that prevent SSRF.
Runtime monitoring of web applications and services can detect anomalous outbound requests indicative of SSRF.
Vulnerability identification processes can discover and record SSRF flaws in web applications.
Network segmentation and egress controls can limit the damage from successful SSRF requests.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Operational threat data describing SSRF campaigns can be used to tighten outbound-request allow-lists and detection rules before attackers exploit them.