VDB-335431 · CVE-2025-64666 · EUVD-2025-202236

Microsoft Exchange Server input validation

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
7.0	$5k-$25k	0.00

Summaryinfo

A vulnerability was found in Microsoft Exchange Server. It has been classified as critical. This affects an unknown function. This manipulation causes input validation. This vulnerability is handled as CVE-2025-64666. The attack can be initiated remotely. There is not any exploit available. It is recommended to apply a patch to fix this issue.

Detailsinfo

A vulnerability classified as critical was found in Microsoft Exchange Server (unknown version). Affected by this vulnerability is an unknown code block. The manipulation with an unknown input leads to a input validation vulnerability. The CWE definition for the vulnerability is CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Improper input validation in Microsoft Exchange Server allows an authorized attacker to elevate privileges over a network.

The weakness was released 12/09/2025 as confirmed security update guide (Website). It is possible to read the advisory at msrc.microsoft.com. This vulnerability is known as CVE-2025-64666. The exploitation appears to be difficult. The attack can be launched remotely. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 01/15/2026).

The vulnerability scanner Nessus provides a plugin with the ID 278114 (Security Updates for Microsoft Exchange Server (December 2025)), which helps to determine the existence of the flaw in a target environment.

Applying a patch is able to eliminate this problem. A possible mitigation has been published immediately after the disclosure of the vulnerability.

The vulnerability is also documented in the databases at Tenable (278114) and EUVD (EUVD-2025-202236). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Type

Groupware Software

Vendor

Microsoft

Name

Exchange Server

License

commercial

Website

Vendor: https://www.microsoft.com/

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.5
VulDB Meta Temp Score: 7.0

VulDB Base Score: 7.5
VulDB Temp Score: 6.5
VulDB Vector: 🔒
VulDB Reliability: 🔍

Vendor Base Score (Microsoft): 7.5
Vendor Vector (Microsoft): 🔒

NVD Base Score: 7.5
NVD Vector: 🔒

CNA Base Score: 7.5
CNA Vector (Microsoft): 🔒

CVSSv2info

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
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Unlock	Unlock	Unlock	Unlock	Unlock	Unlock

VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Input validation
CWE: CWE-20
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Unproven

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Nessus ID: 278114
Nessus Name: Security Updates for Microsoft Exchange Server (December 2025)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Patch
Status: 🔍

Reaction Time: 🔒
0-Day Time: 🔒
Exposure Time: 🔒

Timelineinfo

12/09/2025 VulDB entry created
12/09/2025 +0 days Advisory disclosed
12/09/2025 +0 days Countermeasure disclosed
01/15/2026 +36 days VulDB entry last update