VDB-178612 · CVE-2021-34523 · GCVE-0-2021-34523

Microsoft Exchange Server up to 2019 CU9 ProxyShell

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.
9.0	$0-$5k	0.00

Summaryinfo

A vulnerability classified as very critical was found in Microsoft Exchange Server 2013 CU23/2016 CU19/2016 CU20/2019 CU8/2019 CU9. Impacted is an unknown function. Executing a manipulation can lead to an unknown weakness. This vulnerability is tracked as CVE-2021-34523. The attack is restricted to local execution. Moreover, an exploit is present. It is advisable to implement a patch to correct this issue.

Detailsinfo

A vulnerability was found in Microsoft Exchange Server 2013 CU23/2016 CU19/2016 CU20/2019 CU8/2019 CU9 (Groupware Software). It has been declared as very critical. As an impact it is known to affect confidentiality, and integrity.

The weakness was disclosed 07/13/2021 as confirmed security guidance (Website). The advisory is shared for download at portal.msrc.microsoft.com. This vulnerability was named CVE-2021-34523. Technical details are unknown but an exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 10/30/2025).

It is declared as attacked. This issue was added on 11/03/2021 to the CISA Known Exploited Vulnerabilities Catalog with a due date of 11/17/2021:

Apply updates per vendor instructions.

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

Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

Groupware Software

Vendor

Microsoft

Name

Exchange Server

Version

License

commercial

Website

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

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔍
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 9.4
VulDB Meta Temp Score: 9.0

VulDB Base Score: 9.0
VulDB Temp Score: 8.6
VulDB Vector: 🔍
VulDB Reliability: 🔍

Vendor Base Score (Microsoft): 9.9
Vendor Vector (Microsoft): 🔍

NVD Base Score: 9.8
NVD Vector: 🔍

CNA Base Score: 9.0
CNA Vector (Microsoft): 🔍

CVSSv2info

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

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

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

NVD Base Score: 🔍

Exploitinginfo

Class: Unknown
CWE: Unknown
CAPEC: 🔍
ATT&CK: 🔍

Physical: Partially
Local: Yes
Remote: Yes

Availability: 🔍
Status: Attacked

EPSS Score: 🔍
EPSS Percentile: 🔍

KEV Added: 🔍
KEV Due: 🔍
KEV Remediation: 🔍
KEV Ransomware: 🔍
KEV Notice: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍

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

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Patch
Status: 🔍

Reaction Time: 🔍
0-Day Time: 🔍
Exposure Time: 🔍

Timelineinfo

06/09/2021 🔍
07/13/2021 +34 days 🔍
07/13/2021 +0 days 🔍
07/14/2021 +0 days 🔍
10/30/2025 +1569 days 🔍

Sourcesinfo

Vendor: microsoft.com

Advisory: portal.msrc.microsoft.com
Status: Confirmed

CVE: CVE-2021-34523 (🔍)
GCVE (CVE): GCVE-0-2021-34523
GCVE (VulDB): GCVE-100-178612
scip Labs: https://www.scip.ch/en/?labs.20161013

Entryinfo

Created: 07/14/2021 09:22
Updated: 10/30/2025 21:18
Changes: 07/14/2021 09:22 (17), 07/14/2021 09:23 (14), 07/14/2021 09:26 (22), 07/18/2021 06:39 (2), 12/13/2021 11:27 (1), 04/21/2024 20:27 (28), 09/15/2024 13:07 (1), 03/07/2025 21:39 (27), 10/30/2025 21:18 (1)
Complete: 🔍
Cache ID: 216::103