Microsoft Office Remote Code Execution
CVE-2017-11826 is a high-severity improper restriction of operations within the bounds of a memory buffer vulnerability in Microsoft Office from Microsoft, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. CISA added it to the Known Exploited Vulnerabilities catalogue on March 3, 2022, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Check which version of Microsoft Office 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.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Microsoft Office | Not specified in the record | Not stated |
| Microsoft | Office Compatibility Pack | Not specified in the record | Not stated |
| Microsoft | Office Online Server | 2016 | Not stated |
| Microsoft | Office Web Apps Server | 2010; 2013 | Not stated |
| Microsoft | Office Word Viewer | Not specified in the record | Not stated |
| Microsoft | Sharepoint Enterprise Server | 2016 | Not stated |
| Microsoft | Sharepoint Server | 2010; 2013 | Not stated |
| Microsoft | Word | 2007; 2010; 2013; 2016 | 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
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- 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:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | NVD |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
| CVSS 2.0 | 9.3 | High | NVD |
Official description
Microsoft Office 2010, SharePoint Enterprise Server 2010, SharePoint Server 2010, Web Applications, Office Web Apps Server 2010 and 2013, Word Viewer, Word 2007, 2010, 2013 and 2016, Word Automation Services, and Office Online Server allow remote code execution when the software fails to properly handle objects in memory.
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: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2017-11826US Government Resource
Technical write-ups (may include proof of concept)
- 0patch.blogspot.com/2017/11/0patching-pretty-nasty-microsoft-word.htmlExploit
- tarlogic.com/en/blog/exploiting-word-cve-2017-11826/Exploit, Third Party Advisory
Other vulnerabilities in Microsoft Office
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Microsoft Excel Remote Code Execution Exploited
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Microsoft MSHTML Remote Code Execution Exploited
- 7.8 High severity
Microsoft Office Memory Corruption Exploited
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Microsoft Office Remote Code Execution Exploited
- 7.8 High severity
Microsoft Office Use-After-Free Exploited
Recent Improper Restriction of Operations within the Bounds of a Memory Buffer vulnerabilities
- 7.8 High severity
- 7.8 High severity
Linux Kernel PIE Stack Buffer Corruption Exploited
- 9.8 Critical severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
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