CVE-2021-31195: Microsoft Exchange Server Remote Code Execution Vulnerability
Noroxi assessment
Priority: Plan (action score 48/100)
- A ready-made attack module is public (Nuclei); exploiting it takes no special expertise.
- Public proof-of-concept code exists (Exploit-DB / GitHub); there is no record of exploitation in the wild.
- Probability of exploitation in the next 30 days: 73.6% (FIRST EPSS); higher than 99.4% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. No special conditions are required; it is repeatable.
- According to the record, no fixed version is available yet.
Add it to your regular patch cycle. Update when a fix is released; follow the vendor's advisory.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
- Published
- May 11, 2021
- Updated
- Jun 16, 2026
- EPSS
- 73.6% · 99th percentile
- CWE
- CWE-290
Report tools
Action score
48
Add it to your regular patch cycle.
- CVSS
- 26 / 40 · 6.5 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 22 / 30 · 73.6%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · microsoft
- 6.5
- NVD has not scored this yet; the score shown is the CNA’s.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/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.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- Proof of concept exists, no weaponized module
- No fixed version yet
If any of these changes, we'll tell you in the daily email digest.
Is your version affected? Check itNoroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| 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)
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 15.00.1497.018affected
Microsoft Microsoft Exchange Server 2016 Cumulative Update 19
- 15.01.0 and later · before 15.01.2176.014affected
Microsoft Microsoft Exchange Server 2016 Cumulative Update 20
- 15.01.0 and later · before 15.01.2242.010affected
Microsoft Microsoft Exchange Server 2019 Cumulative Update 8
- 15.02.0 and later · before 15.02.0792.015affected
Microsoft Microsoft Exchange Server 2019 Cumulative Update 9
- 15.02.0 and later · before 15.02.0858.012affected
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
Same product
microsoft: all recordsOther highest-scoring records for the same primary product.
- CVE-2021-34523Microsoft Exchange Server Elevation of Privilege VulnerabilityKEV96Now
- CVE-2021-34473Microsoft Exchange Server Remote Code Execution VulnerabilityKEV96Now
- CVE-2021-26855Microsoft Exchange Server Remote Code Execution VulnerabilityKEV96Now
Published before and after this one in the same product
- ← EarlierCVE-2021-28482Apr 13, 2021 · Microsoft Exchange Server Remote Code Execution Vulnerability60This week
- ← EarlierCVE-2021-28483Apr 13, 2021 · Microsoft Exchange Server Remote Code Execution Vulnerability36Monitor
- Later →CVE-2021-31198May 11, 2021 · Microsoft Exchange Server Remote Code Execution Vulnerability32Monitor
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
Proof of concept available
A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.
Evidence
- Nuclei detection template ×1
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 |
|---|---|---|
| Nuclei detection template | Nuclei template CVE-2021-31195 | — |
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.
No dated events beyond publication.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
- CVE-2021-312070 days apartMicrosoft Exchange Server Security Feature Bypass VulnerabilityKEV86Now
- CVE-2021-3119664 days apartMicrosoft Exchange Server Remote Code Execution VulnerabilityKEV74This week
- CVE-2021-2848228 days apartMicrosoft Exchange Server Remote Code Execution Vulnerability60This week
- CVE-2021-2848328 days apartMicrosoft Exchange Server Remote Code Execution Vulnerability36Monitor
Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · public bounty program.
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- A user must open a link or visit a page.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- high · data can be read
- Integrity
- none
- Availability
- none
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- None
- Availability impact
- None
Weakness class (CWE)
CWE-290 · Authentication Bypass by SpoofingCVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/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)
- Exploitation of Trusted IdentifiersCAPEC-21likelihood: High · High
- Exploiting Trust in ClientCAPEC-22likelihood: High · High
- Creating a Rogue Certification Authority CertificateCAPEC-459likelihood: Medium · Very High
- Web Services API Signature Forgery Leveraging Hash Function Extension WeaknessCAPEC-461High
- Signature SpoofCAPEC-473
- Signature Spoofing by MisrepresentationCAPEC-476likelihood: Low · High
- Session Credential Falsification through PredictionCAPEC-59likelihood: High · High
- Reusing Session IDs (aka Session Replay)CAPEC-60likelihood: High · High
ATT&CK techniques
- Masquerading: Invalid Code SignatureT1036.001
- Access Token ManipulationT1134
- Access Token Manipulation:Token Impersonation/TheftT1134.001
- Steal Application Access TokenT1528
- Steal Web Session CookieT1539
- Use Alternate Authentication Material:Web Session CookieT1550.004
- Subvert Trust Controls: Code SigningT1553.002
- Adversary-in-the-MiddleT1557
Change log (0)
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.