Skip to content
Noroxi
CVE-2021-26855· NVD / CVE Program· CNA microsoft

Microsoft Exchange Server Remote Code Execution Vulnerability

CriticalCVSS 9.1 · v3.1KEVWeaponized No fix recorded
Published
Mar 2, 2021
Updated
Aug 19, 2026
EPSS
100.0% · 100th percentile
Follow this CVE

Sign in to follow · You’ll be notified if a followed record enters KEV, gets an exploit or is updated.

Report tools

JSON

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:F/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: May 3, 2022.

Known to be used in ransomware campaigns.

Affected systems

VendorProduct
microsoftexchange server

Using exchange server? Add it to your stack and be the first to know about CVEs like this one. (Email server)

Add to my stack

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 21

    • 15.00.0 and later · before 15.00.1395.012affected

  • Microsoft Microsoft Exchange Server 2013 Cumulative Update 22

    • 15.00.0 and later · before 15.00.1473.006affected

  • Microsoft Microsoft Exchange Server 2013 Cumulative Update 23

    • 15.00.0 and later · before 15.00.1497.012affected

  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 10

    • 15.01.0 and later · before 15.01.1531.012affected

  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 11

    • 15.01.0 and later · before 15.01.1591.018affected

  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 12

    • 15.01.0 and later · before 15.01.1713.010affected

  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 13

    • 15.01.0 and later · before 15.01.1779.008affected

  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 14

    • 15.01.0 and later · before 15.01.1847.012affected

  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 15

    • 15.01.0 and later · before 15.01.1913.012affected

  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 16

    • 15.01.0 and later · before 15.01.1979.008affected

  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 17

    • 15.01.0 and later · before 15.01.2044.013affected

  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 18

    • 15.01.0 and later · before 15.01.2106.013affected

Same product

microsoft: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-34523Microsoft Exchange Server Elevation of Privilege VulnerabilityKEV
    96Now
  • CVE-2021-34473Microsoft Exchange Server Remote Code Execution VulnerabilityKEV
    96Now
  • CVE-2022-41040Microsoft Exchange Server Elevation of Privilege VulnerabilityKEV
    95Now
  • CVE-2020-0688A remote code execution vulnerability exists in Microsoft Exchange software when the software fails to properly handle objects in memory, akKEV
    95Now
  • CVE-2021-42321Microsoft Exchange Server Remote Code Execution VulnerabilityKEV
    93Now
  • CVE-2022-41082Microsoft Exchange Server Remote Code Execution VulnerabilityKEV
    92Now

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 ×3
  • Exploit-DB entry ×4
  • Nuclei detection template ×1
  • Proof-of-concept repository on GitHub ×50

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.

Public exploit evidence
SourceKindDate
Exploit-DB entryremote2021-03-14
Exploit-DB entrywebapps2021-03-11
Exploit-DB entrywebapps2021-05-18
Exploit-DB entrywebapps2021-05-21
Metasploit moduleauxiliary/gather/exchange_proxylogon_collectorMicrosoft Exchange ProxyLogon Collectorauxiliary2021-03-02
Metasploit moduleauxiliary/scanner/http/exchange_proxylogonMicrosoft Exchange ProxyLogon Scannerauxiliary2021-03-02
Metasploit moduleexploit/windows/http/exchange_proxylogon_rceMicrosoft Exchange ProxyLogon RCEexploit2021-03-02
Nuclei detection templateNuclei template CVE-2021-26855 —
Proof-of-concept repository on GitHubstars:52021-03-03
Proof-of-concept repository on GitHubstars:222021-03-03
Proof-of-concept repository on GitHubstars:982021-03-05
Proof-of-concept repository on GitHubstars:352021-03-06

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.

  1. Metasploit-1 d
  2. Published
  3. First PoCsame day
  4. CISA KEV+245 d
  5. TodaySep 29, 2026+2037 d
EPSS, last 120 days

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 researchers

Finders, 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.

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 help

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records