Microsoft Exchange Server Remote Code Execution Vulnerability
- Published
- Jul 14, 2021
- Updated
- Aug 10, 2026
- EPSS
- 100.0% · 100th percentile
- CWE
- CWE-918
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Action score
96
Now
Patch today or shut off access.
- CVSS
- 36 / 40 · 9.1 / 10
- CISA KEV
- 30 / 30 · Listed
- EPSS
- 30 / 30 · 100.0%
CISA SSVC decision
- Exploitation
- active
- Automatable
- yes
- Technical impact
- total
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · microsoft
- 9.1
- NVD has not scored this yet; the score shown is the CNA’s.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:C
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Actively exploited in the wild
CISA added this to its Known Exploited Vulnerabilities catalog on Nov 3, 2021. That signals real attacks, not theory.
Remediation deadline for government agencies: Nov 17, 2021.
Known to be used in ransomware campaigns.
Affected systems
| Vendor | Product | CPE |
|---|---|---|
| microsoft | exchange server | cpe:2.3:a:microsoft:exchange_server |
Using exchange server? Add it to your stack and be the first to know about CVEs like this one. (Email server)
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- microsoft exchange server2013
- microsoft exchange server2016
- microsoft exchange server2019
Versions reported by the vendor
Affected version ranges reported by the assigning authority (microsoft). Independent of NVD's CPE analysis and usually ahead of it.
Microsoft Microsoft Exchange Server 2013 Cumulative Update 23
- 15.00.0 and later · before 15.00.1497.015affected
Microsoft Microsoft Exchange Server 2016 Cumulative Update 19
- 15.01.0 and later · before 15.01.2176.012affected
Microsoft Microsoft Exchange Server 2016 Cumulative Update 20
- 15.01.0 and later · before 15.01.2242.008affected
Microsoft Microsoft Exchange Server 2019 Cumulative Update 8
- 15.02.0 and later · before 15.02.0792.013affected
Microsoft Microsoft Exchange Server 2019 Cumulative Update 9
- 15.02.0 and later · before 15.02.0858.010affected
Same product
microsoft: all recordsOther highest-scoring records for the same primary product.
- CVE-2021-34523Microsoft Exchange Server Elevation of Privilege VulnerabilityKEV96Now
- CVE-2021-26855Microsoft Exchange Server Remote Code Execution VulnerabilityKEV96Now
- CVE-2022-41040Microsoft Exchange Server Elevation of Privilege VulnerabilityKEV95Now
- CVE-2020-0688A remote code execution vulnerability exists in Microsoft Exchange software when the software fails to properly handle objects in memory, akKEV95Now
- CVE-2021-42321Microsoft Exchange Server Remote Code Execution VulnerabilityKEV93Now
- CVE-2022-41082Microsoft Exchange Server Remote Code Execution VulnerabilityKEV92Now
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
No fix version is recorded for this entry. Check the references for vendor advisories.
Exploit status
Weaponized
A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.
Evidence
- Metasploit module ×1
- Nuclei detection template ×1
- Proof-of-concept repository on GitHub ×9
Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.
| Source | Kind | Date |
|---|---|---|
| Metasploit module | exploit/windows/http/exchange_proxyshell_rceMicrosoft Exchange ProxyShell RCEexploit | 2021-04-06 |
| Nuclei detection template | Nuclei template CVE-2021-34473 | — |
| Proof-of-concept repository on GitHub | stars:46 | 2021-08-10 |
| Proof-of-concept repository on GitHub | stars:5 | 2021-08-11 |
| Proof-of-concept repository on GitHub | stars:30 | 2021-08-16 |
| Proof-of-concept repository on GitHub | stars:121 | 2021-09-04 |
| Proof-of-concept repository on GitHub | stars:16 | 2021-11-22 |
| Proof-of-concept repository on GitHub | stars:0 | 2022-05-24 |
| Proof-of-concept repository on GitHub | stars:42 | 2022-06-29 |
| Proof-of-concept repository on GitHub | stars:2 | 2022-11-16 |
| Proof-of-concept repository on GitHub | stars:0 | 2023-10-17 |
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
- Metasploit-100 d
- Published
- First PoC+26 d
- CISA KEV+111 d
- TodaySep 29, 2026+1903 d
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- high · data can be read
- Integrity
- high · data or configuration can be modified
- Availability
- none
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- None
Weakness class (CWE)
CWE-918 · Server-Side Request Forgery (SSRF)CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
nvd-secondary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
—
Noroxi analysis
No Noroxi analysis for this record yet
We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.
We use this product, ask for helpChange log
No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.
References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34473
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34473
- www.zerodayinitiative.com/advisories/ZDI-21-821/
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34473
Vendor advisories and official records. Exploit/PoC links are deliberately left out.