CyberSecBulletin
CVE-2021-34448Exploited in the wildNVD status: Analyzed

Microsoft Windows Scripting Engine Memory Corruption

Published Updated By the CyberSecBulletin desk

CVE-2021-34448 is a high-severity out-of-bounds write vulnerability in Windows 10 Version 1507 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 unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists version 10.0.10240.19003 as the first without the flaw, so updating Windows 10 Version 1507 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on November 3, 2021, which means attacks have been observed in the wild.

Patch now

Attackers are already exploiting this vulnerability, according to CISA.

What to do

  1. Update Windows 10 Version 1507 to 10.0.10240.19003 or a later version.
  2. Update Windows 10 Version 1607 to 10.0.14393.4530 or a later version.
  3. Update Windows 10 Version 1809 to 10.0.17763.2061 or a later version.
  4. CISA's required action: Apply updates per vendor instructions.
  5. Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
  6. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
  7. 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

VendorProductAffected versionsFixed in
MicrosoftWindows 10 Version 150710.0.10240.0 up to, but not including, 10.0.10240.1900310.0.10240.19003
MicrosoftWindows 10 Version 160710.0.14393.0 up to, but not including, 10.0.14393.453010.0.14393.4530
MicrosoftWindows 10 Version 180910.0.17763.0 up to, but not including, 10.0.17763.2061; 10.0.0 up to, but not including, 10.0.17763.206110.0.17763.2061
MicrosoftWindows 10 Version 190910.0.0 up to, but not including, 10.0.18363.167910.0.18363.1679
MicrosoftWindows 10 Version 200410.0.0 up to, but not including, 10.0.19041.111010.0.19041.1110
MicrosoftWindows 10 Version 20H210.0.0 up to, but not including, 10.0.19042.111010.0.19042.1110
MicrosoftWindows 10 Version 21H110.0.0 up to, but not including, 10.0.19043.111010.0.19043.1110
MicrosoftWindows 76.1.0 up to, but not including, 6.1.7601.256616.1.7601.25661
MicrosoftWindows 7 Service Pack 16.1.0 up to, but not including, 6.1.7601.256616.1.7601.25661
MicrosoftWindows 8.16.3.0 up to, but not including, 6.3.9600.200696.3.9600.20069
MicrosoftWindows Server 2008 R2 Service Pack 16.1.7601.0 up to, but not including, 6.1.7601.256616.1.7601.25661
MicrosoftWindows Server 20126.2.9200.0 up to, but not including, 6.2.9200.234096.2.9200.23409
MicrosoftWindows Server 2012 R26.3.9600.0 up to, but not including, 6.3.9600.200696.3.9600.20069
MicrosoftWindows Server 201610.0.14393.0 up to, but not including, 10.0.14393.453010.0.14393.4530
MicrosoftWindows Server 201910.0.17763.0 up to, but not including, 10.0.17763.206110.0.17763.2061
MicrosoftWindows 10 1507before 10.0.10240.1900310.0.10240.19003
MicrosoftWindows 10 1607before 10.0.14393.453010.0.14393.4530
MicrosoftWindows 10 1809before 10.0.17763.206110.0.17763.2061
MicrosoftWindows 10 1909before 10.0.18363.167910.0.18363.1679
MicrosoftWindows 10 2004before 10.0.19041.111010.0.19041.1110
MicrosoftWindows 10 20h2before 10.0.19042.111010.0.19042.1110
MicrosoftWindows 10 21h1before 10.0.19043.111010.0.19043.1110
MicrosoftWindows Rt 8.1Not specified in the recordNot stated
MicrosoftWindows Server 2008r2Not 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
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:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.16.8MediumCNA (microsoft.com)
CVSS 3.18.8HighNVD
CVSS 2.09.3HighNVD

Official description

Scripting Engine Memory Corruption Vulnerability

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Out-of-bounds Write

The product writes data past the end, or before the beginning, of the intended buffer.

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.

More Out-of-bounds Write vulnerabilities (CWE-787)

Timeline

  1. CVE record published.
  2. Added to CISA's Known Exploited Vulnerabilities catalogue.
  3. Deadline for US federal agencies to remediate, set by CISA.
  4. CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
  5. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Other vulnerabilities in Windows 10 Version 1507

All Windows 10 Version 1507 vulnerabilities

Recent Out-of-bounds Write vulnerabilities

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