CyberSecBulletin
CVE-2023-21674Exploited in the wildNVD status: Analyzed

Microsoft Windows Advanced Local Procedure Call (ALPC) Privilege Escalation

Published Updated By the CyberSecBulletin desk

CVE-2023-21674 is a high-severity use after free vulnerability in Windows 10 Version 1809 from Microsoft, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists version 10.0.17763.3887 as the first without the flaw, so updating Windows 10 Version 1809 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on January 10, 2023, 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 1809 to 10.0.17763.3887 or a later version.
  2. Update Windows Server 2019 to 10.0.17763.3887 or a later version.
  3. Update Windows Server 2019 (Server Core installation) to 10.0.17763.3887 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.

Affected products and versions

VendorProductAffected versionsFixed in
MicrosoftWindows 10 Version 180910.0.17763.0 up to, but not including, 10.0.17763.3887; 10.0.0 up to, but not including, 10.0.17763.388710.0.17763.3887
MicrosoftWindows Server 201910.0.17763.0 up to, but not including, 10.0.17763.388710.0.17763.3887
MicrosoftWindows Server 2019 (Server Core installation)10.0.17763.0 up to, but not including, 10.0.17763.388710.0.17763.3887
MicrosoftWindows Server 202210.0.20348.0 up to, but not including, 10.0.20348.148710.0.20348.1487
MicrosoftWindows 10 Version 20H210.0.0 up to, but not including, 10.0.19042.248610.0.19042.2486
MicrosoftWindows 11 version 21H210.0.0 up to, but not including, 10.0.22000.145510.0.22000.1455
MicrosoftWindows 10 Version 21H210.0.19043.0 up to, but not including, 10.0.19044.248610.0.19044.2486
MicrosoftWindows 11 version 22H210.0.22621.0 up to, but not including, 10.0.22621.110510.0.22621.1105
MicrosoftWindows 10 Version 22H210.0.19045.0 up to, but not including, 10.0.19045.248610.0.19045.2486
MicrosoftWindows 10 Version 150710.0.10240.0 up to, but not including, 10.0.10240.1968510.0.10240.19685
MicrosoftWindows 10 Version 160710.0.14393.0 up to, but not including, 10.0.14393.564810.0.14393.5648
MicrosoftWindows Server 201610.0.14393.0 up to, but not including, 10.0.14393.564810.0.14393.5648
MicrosoftWindows Server 2016 (Server Core installation)10.0.14393.0 up to, but not including, 10.0.14393.564810.0.14393.5648
MicrosoftWindows 8.16.3.0 up to, but not including, 6.3.9600.207786.3.9600.20778
MicrosoftWindows Server 2012 R26.3.9600.0 up to, but not including, 6.3.9600.207786.3.9600.20778
MicrosoftWindows Server 2012 R2 (Server Core installation)6.3.9600.0 up to, but not including, 6.3.9600.207786.3.9600.20778
MicrosoftWindows 10 1507before 10.0.10240.1968510.0.10240.19685
MicrosoftWindows 10 1607before 10.0.14393.564810.0.14393.5648
MicrosoftWindows 10 1809before 10.0.17763.388710.0.17763.3887
MicrosoftWindows 10 20h2before 10.0.19042.248610.0.19042.2486
MicrosoftWindows 10 21h2before 10.0.19044.248610.0.19044.2486
MicrosoftWindows 10 22h2before 10.0.19045.248610.0.19045.2486
MicrosoftWindows 11 21h2before 10.0.22000.145510.0.22000.1455
MicrosoftWindows 11 22h2before 10.0.22621.110510.0.22621.1105
MicrosoftWindows Rt 8.1Not specified in the recordNot stated

Version data comes from the organisation that assigned the CVE; 1 further products are omitted here. 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
LowA basic user account is enough.
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:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H. Scored by CNA (microsoft.com).

Official description

Windows Advanced Local Procedure Call (ALPC) Elevation of Privilege Vulnerability

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

The underlying weakness: Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.

How developers prevent this class of flaw

  • Choose a language that provides automatic memory management.
  • When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.

More Use After Free vulnerabilities (CWE-416)

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: no, technical impact: total).
  5. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Recent Use After Free vulnerabilities

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