CyberSecBulletin
CVE-2023-41763Exploited in the wildNVD status: Analyzed

Microsoft Skype for Business Privilege Escalation

Published Updated By the CyberSecBulletin desk

CVE-2023-41763 is a medium-severity server-side request forgery vulnerability in Skype for Business Server 2015 CU13 from Microsoft, with a CVSS 3.1 base score of 5.3 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 6.0.9319.869 as the first without the flaw, so updating Skype for Business Server 2015 CU13 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on October 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 Skype for Business Server 2015 CU13 to 6.0.9319.869 or a later version.
  2. Update Skype for Business Server 2019 CU7 to 7.0.246.530 or a later version.
  3. CISA's required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
  4. Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
  5. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
MicrosoftSkype for Business Server 2015 CU139319.0 up to, but not including, 6.0.9319.8696.0.9319.869
MicrosoftSkype for Business Server 2019 CU72046.0 up to, but not including, 7.0.246.5307.0.246.530
MicrosoftSkype For Business Server2015; 2019Not 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
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
LowSome restricted data can be read.
Integrity
NoneNothing can be modified.
Availability
NoneAvailability is not affected.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N. Scored by CNA (microsoft.com).

Official description

Skype for Business Elevation of Privilege Vulnerability

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

The underlying weakness: Server-Side Request Forgery

The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.

How developers prevent this class of flaw

  • If there is a known list of applications, IP, hostname, and/or domains to which the product is allowed to communicate, then use allowlists to ensure that outgoing requests are restricted to these known entities. The allowlists could be in the application code or possibly enforced by firewalls or network segmentation.
  • If the product is expected to be able to connect to arbitrary IP addresses or domains, consider using a denylist that includes private network addresses, internal domain names, etc. The denylist could be in the application code or possibly enforced by firewalls or network segmentation.

More Server-Side Request Forgery vulnerabilities (CWE-918)

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: partial).
  5. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Recent Server-Side Request Forgery vulnerabilities

Spotted an error? Tell us.