CVE-2023-21529: Microsoft Exchange Server Remote Code Execution Vulnerability
Noroxi assessment
Priority: Now (action score 83/100)
- CISA has confirmed exploitation in the wild (Apr 13, 2026); it is known to be used in ransomware campaigns. Remediation deadline for US federal agencies: Apr 27, 2026.
- Probability of exploitation in the next 30 days: 59.2% (FIRST EPSS); higher than 99.1% of all records.
- Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
- According to the record, no fixed version is available yet.
- Mentioned 2 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Patch today or shut off access. Until a fix is released, restrict access to the affected component and 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 · CISA KEV · FIRST EPSS
- Published
- Feb 14, 2023
- Updated
- Aug 19, 2026
- EPSS
- 59.2% · 99th percentile
- CWE
- CWE-502
Report tools
Action score
83
Now
Patch today or shut off access.
- CVSS
- 35 / 40 · 8.8 / 10
- CISA KEV
- 30 / 30 · Listed
- EPSS
- 18 / 30 · 59.2%
CISA SSVC decision
- Exploitation
- active
- Automatable
- no
- Technical impact
- total
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · microsoft
- 8.8
- NVD has not scored this yet; the score shown is the CNA’s.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/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 Apr 13, 2026. That signals real attacks, not theory.
Remediation deadline for US federal agencies: Apr 27, 2026.
Known to be used in ransomware campaigns.
Get told when this record changes
- In CISA KEV: exploitation in the wild confirmed
- Weaponized exploit exists
- No fixed version yet
If any of these changes, we'll tell you in the daily email digest.
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Noroxi 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)
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 15.00.1497.047affected
Microsoft Microsoft Exchange Server 2016 Cumulative Update 23
- 15.01.0 and later · before 15.01.2507.021affected
Microsoft Microsoft Exchange Server 2019 Cumulative Update 11
- 15.02.0 and later · before 15.02.0986.041affected
Microsoft Microsoft Exchange Server 2019 Cumulative Update 12
- 15.02.0 and later · before 15.02.1118.025affected
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-2023-21763Jan 10, 2023 · Microsoft Exchange Server Elevation of Privilege Vulnerability31Monitor
- ← EarlierCVE-2023-21764Jan 10, 2023 · Microsoft Exchange Server Elevation of Privilege Vulnerability31Monitor
- Later →CVE-2023-21706Feb 14, 2023 · Microsoft Exchange Server Remote Code Execution Vulnerability36Monitor
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.
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.
- Published
- CISA KEV+1153 d
- TodayNov 10, 2026+1365 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).
National notice (Türkiye Cybersecurity Directorate / USOM)
Official security notices citing this record; remediation advice is on the agency's page.
- TR-23-0105 · Feb 23, 2023(Mozilla Firefox Güvenlik Güncellemesi)
- TR-23-0085 · Feb 15, 2023(Microsoft Exchange Server Zafiyeti)
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- A low-privileged account is enough.
- 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
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
Weakness class (CWE)
CWE-502 · Deserialization of Untrusted DataCVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
nvd-secondary
Root cause
Data received over the network is deserialized into the language’s native object format without verifying its source. Code paths inside the object can be triggered during deserialization.
The bug in code
The whole CWE-502 classA representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.
Vulnerable
payload = sock.recv(65536)
job = pickle.loads(payload)Fixed
payload = sock.recv(65536)
if not hmac.compare_digest(sign(payload), header_sig):
raise PermissionError("invalid signature")
job = JobSchema.validate(json.loads(payload))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
—
Change log
No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.
References
Show all references (2 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.