Microsoft SMBv3 Remote Code Execution
CVE-2020-0796 is a critical-severity improper restriction of operations within the bounds of a memory buffer vulnerability in Windows 10 Version 1903 for 32-bit Systems from Microsoft, with a CVSS 3.1 base score of 10.0 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. CISA added it to the Known Exploited Vulnerabilities catalogue on February 10, 2022, 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 Windows 10 Version 1903 for 32-bit Systems 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.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
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
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- 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:N/UI:N/S:C/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 10.0 | Critical | NVD |
| CVSS 3.1 | 10.0 | Critical | CISA (ADP) |
| CVSS 2.0 | 7.5 | High | NVD |
Official description
A remote code execution vulnerability exists in the way that the Microsoft Server Message Block 3.1.1 (SMBv3) protocol handles certain requests, aka 'Windows SMBv3 Client/Server Remote Code Execution Vulnerability'.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Restriction of Operations within the Bounds of a Memory Buffer
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary.
How developers prevent this class of flaw
- Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega, and the Strsafe.h library from Microsoft. These libraries provide safer versions of overflow-prone string-handling functions.
- Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.
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: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Third-party and government advisories
- packetstormsecurity.com/files/156731/CoronaBlue-SMBGhost-Microsoft-Windows-10-SMB-3.1.1-Proof-Of-Concept.htmlThird Party Advisory, VDB Entry
- packetstormsecurity.com/files/156980/Microsoft-Windows-10-SMB-3.1.1-Local-Privilege-Escalation.htmlThird Party Advisory, VDB Entry
- packetstormsecurity.com/files/157901/Microsoft-Windows-SMBGhost-Remote-Code-Execution.htmlThird Party Advisory, VDB Entry
- packetstormsecurity.com/files/158054/SMBleed-SMBGhost-Pre-Authentication-Remote-Code-Execution-Proof-Of-Conce…Third Party Advisory, VDB Entry
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-0796US Government Resource
Technical write-ups (may include proof of concept)
- packetstormsecurity.com/files/156732/Microsoft-Windows-SMB-3.1.1-Remote-Code-Execution.htmlExploit, Third Party Advisory, VDB Entry
- packetstormsecurity.com/files/157110/SMBv3-Compression-Buffer-Overflow.htmlExploit, Third Party Advisory, VDB Entry
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