Microsoft Exchange Server Validation Key Remote Code Execution
CVE-2020-0688 is a high-severity improper authentication vulnerability in Microsoft Exchange Server 2013 from Microsoft, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected Microsoft Exchange Server 2013 versions: Cumulative Update 23. The record does not name a fixed version, so check the vendor advisory. CISA added it to the Known Exploited Vulnerabilities catalogue on November 3, 2021, which means attacks have been observed in the wild, including in ransomware campaigns.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Check which version of Microsoft Exchange Server 2013 you run against the affected versions below, and install the vendor's latest release.
- CISA's required action: Apply updates per vendor instructions.
- Read the advisory on portal.msrc.microsoft.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Microsoft Exchange Server 2013 | Cumulative Update 23 | Not stated |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 3 | Not specified in the record | Not stated |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 14 | Not specified in the record | Not stated |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 15 | Not specified in the record | Not stated |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 4 | Not specified in the record | Not stated |
| Microsoft | Microsoft Exchange Server 2010 Service Pack 3 Update Rollup 30 | Not specified in the record | Not stated |
| Microsoft | Exchange Server | 2010; 2013; 2016; 2019 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.8 | High | NVD |
| CVSS 3.1 | 8.8 | High | CISA (ADP) |
| CVSS 2.0 | 9.0 | High | NVD |
Official description
A remote code execution vulnerability exists in Microsoft Exchange software when the software fails to properly handle objects in memory, aka 'Microsoft Exchange Memory Corruption Vulnerability'.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Authentication
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
How developers prevent this class of flaw
- Use an authentication framework or library such as the OWASP ESAPI Authentication feature.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Third-party and government advisories
- zerodayinitiative.com/advisories/ZDI-20-258/Third Party Advisory, VDB Entry
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-0688US Government Resource
Technical write-ups (may include proof of concept)
- packetstormsecurity.com/files/156592/Microsoft-Exchange-2019-15.2.221.12-Remote-Code-Execution.htmlExploit, Third Party Advisory, VDB Entry
- packetstormsecurity.com/files/156620/Exchange-Control-Panel-Viewstate-Deserialization.htmlExploit, Third Party Advisory, VDB Entry
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