Home/CVE/Microsoft Exchange Server Security Feature Bypass Vulnerability
CVE

CVE-2021-31207

Microsoft Exchange Server Security Feature Bypass Vulnerability

Microsoft Exchange Server Security Feature Bypass Vulnerability.

MEDIUM · CVSS 6.6 ⚠ CISA KEV EPSS 0.93835 Ransomware: known
Act now
  • Listed on CISA KEV (known exploited in the wild)
  • Linked to known ransomware campaigns
  • SSVC exploitation status: active
  • EPSS ≥ 0.50 - high probability of exploitation in the next 30 days
  • EPSS percentile: top 0% of all CVEs by exploitation likelihood
  • Public exploit or PoC is available
Sigma rules10 YARA rules0
⬢

Required Remediation

Apply updates per vendor instructions.

◆

Threat Actors Linked

13
actorALPHV / BlackCat
actorAPT35
actorBianLian
actorDarkSide / BlackMatter
actorFIN7
actorGALLIUM
⬡

Weakness Classification

CWE-434Unrestricted Upload of File with Dangerous Type
CWE-434Unrestricted Upload of File with Dangerous Type
▤

Affected Products & Versions

1
microsoft exchange serverall versions
⚠

Public Exploits & PoCs

1
pocpacketstormsecurity.com · Microsoft-Exchange-ProxyShell-Remote-Code-Execution.htmlpacketstormsecurity.com
◈

Detection Rules (IDS/IPS)

9
et-openET EXPLOIT Microsoft Exchange Pre-Auth Path Confusion M2 (CVE-2021-31207)attempted-admin
et-openET EXPLOIT Vulnerable Microsoft Exchange Server Response (CVE-2021-31207)attempted-admin
et-openET EXPLOIT Microsoft Exchange Pre-Auth Path Confusion M1 (CVE-2021-31207)attempted-admin
et-openET EXPLOIT Microsoft Exchange SUID Disclosure via SSRF Inbound M1 (CVE-2021-31207)attempted-admin
et-openET EXPLOIT Microsoft Exchange SUID Disclosure via SSRF Inbound M2 (CVE-2021-31207)attempted-admin
snort-communitySERVER-WEBAPP Microsoft Exchange autodiscover server side request forgery attemptattempted-admin
Open rulesets (ET Open, Snort Community, abuse.ch) link to source. Commercial rulesets are reference-only.
◈

Sigma Hunt Rules

10
Exact rules name this CVE ID. Product rules name an affected product in their title. Related rules cover techniques used by actors who exploited this CVE. Showing the most relevant matches; the complete related set is on the full drill-down.
relatedcriticalBitbucket Unauthorized Full Data Export Triggered
relatedcriticalBitbucket Unauthorized Access To A Resource
relatedcriticalAntivirus Exploitation Framework Detection
relatedcriticalAntivirus Password Dumper Detection
relatedcriticalAntivirus Ransomware Detection
relatedcriticalWebshell Remote Command Execution
▣

Scoring & Timeline

6.6
MEDIUM · CVSS v3.1 · secure@microsoft.com
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD11 May 2021 · 07:15 PM
CVSS VectorCVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
SSVC triage · cisa-vulnrichment
Exploitation
active
Automatable
no
Technical impact
total
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
⚑

Vendor Advisories

4
cisaKEV-CVE-2021-31207
msrcCVE-2021-31207Security Feature Bypass
splunk-security-contentd436f9e7-0ee7-4a47-864b-6dea2c4e2752
splunk-security-content0f03423c-7c6a-11eb-bc47-acde48001122
🔗

References & Sources

3
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207PatchVendor Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-819/Third Party AdvisoryVDB Entry
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31207US Government Resource
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