VulnerabilityPublished 19 Feb 2025Updated 13 Feb 2026

CVE-2025-21355: Microsoft Bing · Missing Authentication

Affects Microsoft BingSource CVE Database V5

Public exploit available · CVSS 8.6 High.

Data as of 26 Oct 2026, 12:55 UTC

CVSS 3.1 base score

8.6High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 1.6% chance of exploitation in 30 days – higher than 76% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N/E:P/RL:O/RC:C

Base metrics

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Changed
Confidentiality: High
Integrity: None
Availability: None

Temporal metrics

Exploit Code Maturity: Proof-of-Concept
Remediation Level: Official Fix
Report Confidence: Confirmed

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.
Exploit Code Maturity: Proof-of-Concept: Proof-of-concept exploit code is available, or an attack demonstration is not practical for most systems. The code or technique is not functional in all situations and may require substantial modification by a skilled attacker.
Remediation Level: Official Fix: A complete vendor solution is available. Either the vendor has issued an official patch, or an upgrade is available.
Report Confidence: Confirmed: Detailed reports exist, or functional reproduction is possible (functional exploits may provide this). Source code is available to independently verify the assertions of the research, or the author or vendor of the affected code has confirmed the presence of the vulnerability.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 Feb 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: evidence found.
CVSS exploit maturity: proof of concept public
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CVSS vector, the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

AI-suggested

Immediate monitoring for official Microsoft security advisories and patches related to CVE-2025-21355 is critical; apply updates promptly once available.
Until patches are released, restrict network access to Microsoft Bing services from internal networks where feasible, using firewalls or proxy controls to limit exposure.
Implement network segmentation to isolate systems that interact with Bing services, reducing lateral movement risk if exploitation occurs.
Deploy anomaly detection and intrusion prevention systems to identify unusual network traffic or behavior associated with unauthorized code execution attempts.
Review and tighten authentication and access controls on any integrated Bing service components within enterprise environments.
Conduct security awareness training to inform IT staff about this vulnerability and the importance of rapid patching and monitoring.
Engage with Microsoft support channels for guidance and potential mitigations specific to organizational deployments.
Consider temporary disabling or limiting Bing service features that expose critical functions until the vulnerability is resolved.
Maintain comprehensive logging and audit trails for Bing service interactions to facilitate incident detection and forensic analysis if exploitation occurs.

Description

Missing Authentication for Critical Function in Microsoft Bing allows an unauthorized attacker to execute code over a network

Impact

For European organizations, the primary impact of CVE-2025-21355 is the potential unauthorized execution of code within Microsoft Bing services, which could lead to significant data confidentiality breaches. Organizations using Bing for internal or external search, data aggregation, or integrated services might expose sensitive corporate or user data to attackers. The lack of authentication means attackers can exploit this vulnerability remotely without any credentials, increasing the attack surface. While integrity and availability are not directly impacted, the confidentiality breach alone can result in regulatory non-compliance, reputational damage, and financial losses under GDPR and other data protection laws. Additionally, attackers could leverage this vulnerability as a foothold for further attacks within enterprise networks, especially if Bing services are integrated with internal systems. The absence of known exploits currently provides a window for proactive mitigation, but the high severity score indicates a critical need for vigilance. European organizations with high dependency on Microsoft cloud and search services must prioritize monitoring and protective measures to mitigate potential exploitation.

CWE-306Missing Authentication for Critical Function (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #21OWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.
Architecture and Design
Divide the software into anonymous, normal, privileged, and administrative areas. Identify which of these areas require a proven user identity, and use a centralized authentication capability.
Architecture and Design
For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks…
Architecture and Design
Where possible, avoid implementing custom, "grow-your-own" authentication routines and consider using authentication capabilities as provided by the surrounding framework, operating system, or environment.
OWASP Cheat Sheets
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V1.2.3 (opens in a new tab)
V1.2.2 (opens in a new tab)
V1.2.4 (opens in a new tab)
Attack patterns
Choosing Message Identifier (opens in a new tab)
Force the System to Reset Values (opens in a new tab)
Using Unpublished Interfaces or Functionality (opens in a new tab)
Cross Site Request Forgery (opens in a new tab)
Communication Channel Manipulation (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21355 (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 14 Feb 2026, 08:44 UTC

WeaknessesCWE-306

Technical details

References

Community reviews

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