Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2025-21355 is a high-severity Missing Authentication for Critical Function (CWE-306) vulnerability in Microsoft Bing. Its CVSS base score is 8.6 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 25% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-14 (Permitted Actions Without Identification or Authentication) and IA-2 (Identification and Authentication (Organizational Users)) — 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-2025-21355 is a missing authentication for critical function vulnerability, tracked under CWE-306, that affects Microsoft Bing. The flaw carries a CVSS 3.1 score of 8.6 and permits an unauthenticated network attacker to execute code remotely, with the attack vector reflecting network access, low complexity, no required privileges or user interaction, changed scope, high confidentiality impact, and no integrity or availability effects.
An unauthorized attacker can exploit the issue over the network to achieve remote code execution against the affected Bing component, potentially exposing sensitive data across security boundaries without any authentication.
The Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21355 supplies official guidance on patches and mitigation steps. The associated EPSS score has remained flat at 0.0696 with no material increase since disclosure.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-4643
Vulnerability Data
Missing Authentication for Critical Function in Microsoft Bing allows an unauthorized attacker to execute code 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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- 6 hardening rules · 3 OS baselines
V6.2.3V6.4.4V10.4.16V12.1.3
Mitigating Controls (NIST 800-53 r5) AI
Directly mandates unique identification and authentication of users before access to functions requiring identity.
Extends the same authentication requirement to non-organizational users accessing critical functionality.
Requires authentication of services before they can invoke or expose critical functions.
Explicitly identifies and limits actions permitted without authentication, preventing critical functions from being exposed.
Access enforcement requires prior authentication before any authorization decision for critical functions.
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.
Directly requires authentication of users/services/hardware, which eliminates missing authentication for critical functions.
Managing identities and credentials is a prerequisite for authentication but does not itself enforce it on critical functions.
Defining and enforcing authorizations assumes prior authentication and therefore only partially mitigates the absence of authentication.
Protecting networks from unauthorized access can be undermined by missing authentication but does not address the root authentication gap.
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.
The control explicitly calls for authentication before any critical function is reached, eliminating the possibility of bypassing authentication for high-value operations.
Mandating authentication requirements for critical functions at the requirements-gathering stage ensures that essential operations are not left unprotected by missing login or verification mechanisms.
Mandating authentication for network services and critical functions stops attackers from invoking sensitive operations without credentials, closing gaps where authentication is absent for important capabilities.
Security engineering principles insist on authentication and authorization for every critical function, eliminating entry points that lack any access control mechanism.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (2 rules)
- V-248585 OL 8 must require reauthentication when using the "sudo" command. prevents CWE-306
- V-248827 OL 8 must not have the rsh-server package installed. prevents CWE-306
RHEL 7 (2 rules)
- V-204442 The Red Hat Enterprise Linux operating system must not have the rsh-server package installed. prevents CWE-306
- V-237635 The Red Hat Enterprise Linux operating system must require re-authentication when using the "sudo" command. prevents CWE-306
RHEL 8 (2 rules)
- V-230492 RHEL 8 must not have the rsh-server package installed. prevents CWE-306
- V-237643 RHEL 8 must require re-authentication when using the "sudo" command. prevents CWE-306