CVE-2021-31196: Microsoft Exchange Server Information Disclosure Vulnerability

59

High

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

CISA KEV · Aug 21, 2024

How the score was calculated

Confirmed exploitation (CISA KEV)+35
EPSS 54.1% (30-day exploitation probability)+15
Technical severity (high)+6
Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Confirmed

CISA KEV, listed Aug 21, 2024

EPSS FIRST

54.06%

ahead of 99% of scored CVEs · Oct 14, 2026

Affects

Microsoft

Exchange Server and 5 more

CVSS base

7.2

High · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

Active

none · proof-of-concept · active

Automatable

Yes

can an attacker script the kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

Documented patch — msrc.microsoft.com (NIST National Vulnerability Database)
Documented patch — portal.msrc.microsoft.com (NIST National Vulnerability Database)

CISA required action CISA

Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

US federal deadline: Sep 11, 2024 — passed 764 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Microsoft Exchange Server, Microsoft Microsoft Exchange Server 2013 Cumulative Update 23, Microsoft Microsoft Exchange Server 2016 Cumulative Update 20…).
Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
Apply the fixed version or the patch documented under Remediation.
EPSS ahead of 99% of scored CVEs: prioritize it in the patch queue.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Microsoft	Exchange Server	version 2013-cumulative_update_23version 2016-cumulative_update_20version 2016-cumulative_update_21version 2019-cumulative_update_10version 2019-cumulative_update_9	Vulnerable	NIST National Vulnerability Database
Microsoft	Microsoft Exchange Server 2013 Cumulative Update 23	≥ 15.00.0 and < 15.00.1497.023	Vulnerable	CVE Program (cve.org) e CISA ADP
Microsoft	Microsoft Exchange Server 2016 Cumulative Update 20	≥ 15.01.0 and < 15.01.2242.012	Vulnerable	CVE Program (cve.org) e CISA ADP
Microsoft	Microsoft Exchange Server 2016 Cumulative Update 21	≥ 15.01.0 and < 15.01.2308.014	Vulnerable	CVE Program (cve.org) e CISA ADP
Microsoft	Microsoft Exchange Server 2019 Cumulative Update 10	≥ 15.02.0 and < 15.02.0922.013	Vulnerable	CVE Program (cve.org) e CISA ADP
Microsoft	Microsoft Exchange Server 2019 Cumulative Update 9	≥ 15.02.0 and < 15.02.0858.015	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

High

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
7.2	CVSS 3.1	High	1.2	5.9	secure@microsoft.com via NIST National Vulnerability Database
7.2	CVSS 3.1	High	1.2	5.9	nvd@nist.gov via NIST National Vulnerability Database
7.2	CVSS 3.1	High	—	—	microsoft via CVE Program (cve.org) e CISA ADP
6.5	CVSS 2.0	Medium	8.0	6.4	nvd@nist.gov via NIST National Vulnerability Database

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H (score shown at the top: secure@microsoft.com)

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

Listed

Aug 21, 2024

Federal deadline

Sep 11, 2024

passed 764 day(s) ago

Ransomware use

Unknown

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

EPSS over time FIRST

Oct 12, 2026 → Oct 14, 2026 · 3 reading(s) · max 54.06%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Hunt retroactively in logs from before Aug 21, 2024 (KEV listing): exploitation may have started earlier.

web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

2026
Fix documented
Oct 13, 2026 · NIST National Vulnerability Database
Affected products added · microsoft/exchange server
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · Published → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record published
Oct 13, 2026
Affected products added · microsoft/microsoft exchange server 2013 cumulative update 23, microsoft/microsoft exchange server 2016 cumulative updat
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
CVSS changed · 7.2
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Source status changed · → Published
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Added to CISA KEV (detected)
Oct 13, 2026 · CISA Known Exploited Vulnerabilities
Record created in this database
Oct 13, 2026 · CISA Known Exploited Vulnerabilities
2024
Added to CISA KEV catalog
Aug 20, 2024 · CISA
2021
CVE published
Jul 14, 2021 · microsoft

Source activity

Repeated readings are counted rather than listed.

2× References added · Oct 13, 2026 – Oct 13, 2026
1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

3 on the record

portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31196
Patch, Vendor Advisory, NIST National Vulnerability Database
msrc.microsoft.com/update-guide/vulnerability/CVE-2021-31196
vendor-advisory, patch, Patch, Vendor Advisory, CVE Program (cve.org) e CISA ADP
www.cisa.gov/known-exploited-vulnerabilities-catalog
US Government Resource, NIST National Vulnerability Database

Elsewhere on this site

Microsoft
every CVE for this vendor

2024-08
what else CISA listed that month

Related CVEs (same products)

High CVE-2026-96940 Weak authorization in Microsoft Exchange Server allows an authenticated attacker to elevate... 13d
Critical CVE-2026-69641 Microsoft Exchange Server Elevation of Privilege Vulnerability Sep 8, 2026
Medium CVE-2026-69382 Microsoft Exchange Server Information Disclosure Vulnerability Sep 8, 2026
High CVE-2026-69380 Microsoft Exchange Server Elevation of Privilege Vulnerability Sep 8, 2026
Medium CVE-2026-69375 Microsoft Exchange Server Tampering Vulnerability Sep 8, 2026
High CVE-2026-69378 Microsoft Exchange Server Denial of Service Vulnerability Sep 8, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No CWE classification.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-31196 is "Microsoft Exchange Server Information Disclosure Vulnerability", rated High. It affects Exchange Server (Microsoft); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 7.2 describes technical severity. EPSS 54.06% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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