CVE-2025-21355
Published: 19 February 2025
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 8.4% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 AC-14 (Permitted Actions Without Identification or Authentication) and IA-8 (Identification and Authentication (Non-organizational Users)).
Deeper analysis
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.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-4643
Vulnerability details
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 TechniquesAI
Why these techniques?
The vulnerability is a missing authentication for a critical function in the public-facing Microsoft Bing service, directly enabling unauthenticated remote code execution over the network with no privileges or user interaction required, which maps to exploitation of public-facing applications.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly addresses missing authentication for critical functions by explicitly identifying and limiting permitted actions without identification or authentication.
Requires unique identification and authentication for non-organizational users, preventing unauthorized network access to critical functions in public-facing services like Microsoft Bing.
Mandates timely identification, reporting, and correction of flaws such as this missing authentication vulnerability through testing and patching.